If the Central London changes were my plan

I enter the mind of TfL and try an inbox train of though rather than out-of-the-box.
I also decide to affect routes not in Central to add a bit more complexion.
How I would've dealt with the situation:

I thought about the 19 deeply enough that 38 came into mind. These routes have for a long time shared a common section between Islington and Hyde Park. Now that money is a big issue, I quickly came with a calculator to see how I could've dealt the situation for better or worse. I acknowledge some of the existing links and history but what happens when I toss that aside?

Finsbury/Islington
Hackney/Bethnal Green
Instead of faffing with the 19 from the Battersea end, let's do it this way.
Instead of withdrawing the 48, how about kill different birds with a rock?

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19: Rerouted at Islington Green to Hackney Central as per 38.

38: All journeys through to Clapton Pond.

73: Extended from Stoke Newington to Northumberland Park

476: Withdrawn.

Reroute the 263 at Holloway via the 4 to Highbury Barn then onto Islington Green.

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8: Routed at Bow Church to Stratford Bus Station

26: Rerouted at Liverpool Street via Bethnal Green instead of Hackney Road. Routed down Victoria Park Road in Hackney towards Central.
48: Frequency reduced

241: Extended from Stratford City via Hackney Wick then per 277 to Dalston Junction.

388: Withdrawn
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30: Peak frequency reduced from 6-9 to every 8
277: Extended to Holloway via Holloway Road and Highbury & Islington.
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This adds salt in the wound for the loss of 19, but can be done with a hopper from 4/263 to Islington Green for a 19/38 into Central London. 

Holloway Road gains a link to East London plus retains a level of service, not as high as previously with the 263. Route 38's frequency isn't suitable for resources outside peak hours, the decision to extend route 19 over it reduces buses required whilst keeping the corridor at the same frequency.

Night route N19 will be unchanged and remains as a Finsbury Park to Clapham Junction route.
Night route N26 will be unchanged and remains as a Chingford via Hackney Road to Trafalgar Square route.

Current individual frequencies and buses required:

19 (every 8, 26), 38 (every 3-4 §, 52), 
73 (every 5, 34), 476 (every 8, 21)
263 (every 10, 18), 277 (every 6-7, 23)
§ every other one bus makes it to Clapton Pond

8 (every 6-7*, 33), 26 (every 10, 16), 48 (every 10, 19)
241 (every 10, 10), 388 (every 12, 16).
* Peak frequency every 6, then extra peak journeys

Total: 268.

Proposed individual frequencies and peak buses required:

19 (every 8-9, 25), 38 (every 8-9, 26), 73 (every 3-4, 45), 
263 (every 10, 20), 277 (every 6-7 §, 27)

§ every other one bus makes it to Holloway at every 12-14

8 (every 6-7*, 36-37), 26 (every 10, 16), 
48 (every 12, 16), 241 (every 10, 19)
* Every 12-14 a bus will make it to Stratford. Peak frequency every 6, then extra peak journeys
Total: 231.

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Hammersmith/Chelsea/Putney/Ladbroke Grove

Likewise, instead of bringing in the 311 and chopping off both 11/19 from Battersea residents, here's a cleaner approach to do the same thing.

9: Frequency increased

11: Shortened to run Victoria Coach Station to Liverpool Street
14: Frequency increased
18: Frequency decreased

23: Reformed to run Fulham Broadway via Victoria, Paddington, Ladbroke Grove, Stonebridge Park to Wembley Stadium.

414: Withdrawn

This keeps route 14 with an aide to Marble Arch albeit being itself. Fulham/Putney residents still have a way of making into Marble Arch via hopper onto 23 at Hyde Park Corner. In compensation, route 9 can have a frequency increase.

I explored the option of giving shorts to the 14 over the range of Putney Bridge to Piccadilly Circus though there isn't a satisfactory saving compared to just upping 14's frequency as a whole.

If need be, the 11 can be sent to Pimlico Grosvenor Gardens which requires a restructuring to the 24. I'm not ready to touch that and receive huge flak for it.

Current frequency and buses required

9 (every 7-8, 18), 
11 (every 10, 22), 
14 (every 8, 25), 
18 (every 4, 44), 
23 (every 8, 24), 
414 (every 8, 23)
Total PVR: 156

Proposed frequency and buses required

9 (every 6, 23), 
11 (every 10, 16), 
14 (every 6, 34)
18 (every 6, 37), 
23 (every 9, 26)
Total PVR: 136

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Central London:

I thought long and deeply about route 53. Then came to a conclusion.

6: Cut to Piccadilly Circus from Aldwych

94: Cut from Piccadilly Circus to Oxford Circus Conduit Street.
98: Rerouted to Russell Square

3: Stand reassigned to Whitehall Horse Guards
53: Rerouted at Elephant to Aldwych as per 172

172: Withdrawn
453: Peak frequency reduced from every 4-5 to every 7-8.
X53: Limited stop peak-only express calling at Woolwich, Blackheath Royal Standard, Deptford Bridge, New Cross and New Cross Gate Stations, New Cross Bus Garage, Old Kent Road Tesco, Elephant & Castle, St Thomas' Hospital, Trafalgar Square, Oxford Circus, Great Portland Street and Marylebone. Frequency every 20.

Night variations of non-24 hour routes involved won't be changed.

Whilst keeping the Great Portland Street link and giving 7 a link to Piccadilly again since the loss of 23, I thought of withdrawing the 453 from the place not that I desire to but in the name of cost cutting. As a result I also extended 159 back to Paddington, not the Basin. I added 59 to the mix to keep the PVR levels between them similar, otherwise 159's PVR would basically be 40.
I resolved the idea of not getting the 53/453 hopper on time by adding an X53 to the mix, though it serves as less stops but as much popular stops where applicable. Rerouteing the 53 to Waterloo means it's still a central link and still connected to New Cross, though unfortunately not aiding 453 beyond Elephant to Lambeth North.

I admit in rerouting the 7 there's a loss of the Oxford Street link, but would rather Oxford Circus via Marylebone or a cut to Marble Arch? Thank goodness pedestrianisation didn't go ahead.

Current peak frequency and buses required

3 (every 8, 20),  
6 (every 7-8, 24), 
53 (every 7-8, 34),
94 (every 6, 25), 
98 (every 7-8, 23),
172 (every 10-11, 18), 
453 (every 5*, 36)
* Off-peak frequency at every 7-8
Total PVR: 180

Proposed frequency and buses required

3 (every 8, 19), 
6 (every 7-8, 20),
53 (every 7-8, 32), 
94 (every 6, 23), 
98 (every 7-8, 23)
453 (every 7-8, 24), 
X53 (every 20 with the flow, 8)
Total PVR: 149

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City of London & other Central London changing:

Then the last set of changes.

1: Cut at Elephant & Castle. Extended as per 199 to Bellingham Catford Bus Garage
25: Rerouted between Bank and Aldgate via Fenchurch Street.
40: Frequency reduced.
45: Curtailed to Clerkenwell Green.
100: Routed westbound at Tower Gateway via RV1 to London Bridge, then to Liverpool Street via 35. Extended to Blackfriars then Embankment as per 388.
188: Night service routed via Salter and Redriff Roads, renumbered N188 if need be.
199: Withdrawn.
343: Curtailed at Elephant & Castle.
RV1: Withdrawn.
N37: Night time of 37 extended via Surrey Quays to Canada Water via 381.
N381: Withdrawn.

Bottom two changes can be simplified by only extending N37 to Rotherhithe.
Night routes N1 and N199 unchanged.
This gives East London another link to (nearly) Trafalgar Square in the form of 100 and making it slightly more useful whilst also retaining the link with Blackfriars.
No need to increase 35's frequency as the loss of 40 was avoided.
One less route serving Holborn, though this means for routeing purposes the 1 would double run Canada Water and Surrey Quays as a result, preferably in a clockwise motion (Canada before Surrey) towards Elephant and anti-clockwise towards Lewisham.

Current peak frequency and buses required

1 (every 10, 15), 
40 (every 8, 19), 
45 (every 10, 21), 
100 (every 12, 9)
199 (every 12, 12), 
343 (every 7-8, 22), 
RV1 (every 20, 6)
Total PVR: 119

Proposed peak frequency and buses required

1 (every 10, 21), 
40 (every 10, 16), 
45 (every 10, 17), 
100 (every 12, 14)
343 (every 7-8, 17)
Total PVR: 85

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Proposed Grand Total PVR: -132.

Note: These are all rough frequencies and aren't perfect. I'm human so if there's something I input incorrectly, well I'm human.

Postscript bloopers:

I have thought of alternatives such as:

7 to Vauxhall (but replacing what? Just an aide to 36)

6 to Vauxhall ( ^, but no)

7 to Aldwych via Regent Street (hmm)

7 to Fulham Broadway (adds quite a bit of time, not a desirable amount of time)
7 to Trafalgar Square

311 to Elephant & Castle then somewhere in the City (needlessly cutting C10)
53 to Oxford Circus, or Regent Street
453 to Oxford Circus

How I worked some of my calculations: 

27 PVR of 476 section, Stoke to NP. 221 mins round time OC-NP. 45 mins + 39 mins  for 476 section

137 mins round time 73 common, PVR of 18

Total PVR of 45 (18 + 27)

Morning: 48 mins (X - Hyde Park Corner), 47 mins (HPC - Putney Bridge)

Afternoon: 43 mins (Putney - HPC), 50 mins (HPC - X)

14-15 mins Fulham Broadway - Putney Bridge

Rough swaps: 33 from Ham and 28 to Ham.

43-33=10. 47-28=19. 10+19=29. 29/freq=basically_4

(29)-33=-4. (32)-28=4

30 mins Wembley-Kensal either way
35-37 mins Ladbroke-Marble

29-32 mins Victoria to Fulham either way.

12-13 mins Victoria to Marble.
Total: 228 (inc. stand time)

11 mins BN-Streatham either way

44 mins Dalston to Stratford City

60 mins TL-Canada either way

Calcs and dat yh.