Indeed, the largest concentration of such buses is that currently run by Sovereign on the 13 - which still has no date published to lose its Routemasters, although London United's large order for 58 Scania Omnidekkas will unfortunately include enough for the 13. With a delivery window stretching between August and November, it's just a question of whether the 13 will beat the 159 and 38 to be the last 'real' route. If the Heritage Route(s) are set to start in October, that could end up being one hell of a month.

Instead of spending yet more tax-extorted money on tourist trifles, I suppose it's beyond them just to simply cancel the conversion of just one route - i.e. the 38, which fulfils all the functions you'd want of a tourist service (sightseeing) as well as the more important, if mundane role of conveying large numbers of people from workplace to railheads, shops and home. To that end, the responsibility is on TfL to make sure these services are as close to normal as possible. We don't want Disney routes with Dick van Dyke on the platform, thank you. In a crucially important move that has relieved sceptics (like me), early plans to impose a surcharge on farepayers and Travelcard holders would appear to have been shelved.

I was sketching out what I'd recommend for these routes (using the only two low numbers currently vacant) and came up with the following patterns; let's see what the real things look like in a few months' time.
Route 129 - PUTNEY BRIDGE STATION via 14 to Hyde Park Corner, 19 to Tottenham Court Road, 73 to Angel and 19 to HIGHBURY & ISLINGTON. (serves the riverside, the museums, Harrods, Harvey Nichols, Hyde Park, Piccadilly and the ends of Oxford Street (while not serving Oxford Street itself, as per mandate), then taking rush-hour passengers to Euston and Kings Cross St Pancras, and after that through Islington to a convenient terminus that's not too bedevilled by traffic or too far into ropey areas).
Route 135 - NOTTING HILL GATE via 52 to High Street Kensington, 9 to Aldwych and RV1 to Tower Gateway and ALDGATE. (serves Kensington, the museums, Harrods, Harvey Nichols, Hyde Park, Piccadilly, Trafalgar Square and theatreland, caters for Charing Cross, Waterloo and London Bridge commuters and then takes in the London Eye (if it's still around!), the Tate Modern, Tower Bridge, the Tower of London and the Gherkin).
I'd give the former to London General at Putney and the latter to Stagecoach East London at Bow - both garages are professional and capable. I have no idea who's tendered for the routes in reality, so any bias (as if!) is my own. The buses would receive 1933 London Transport livery and retain their fleetnumbers (in gold leaf, naturally), with all hopper windows replaced by proper wind-down versions that actually let air circulate. I'd even spring for wheelchair lifts to be installed in the centre of the buses - it's been done before, after all, by London Coaches.

For now, Trafalgar Square is the location of this picture, where we see RM 346 (SVS 615, ex WLT 346) on the 159 and RM 441 (LDS 341A, ex WLT 441) on the 13 - both to Euro 2 emissions spec with Cummins B series engines and Allison T270 gearboxes. As London's centre, Trafalgar Square must have a Routemaster service. My proposal would serve there - will Ken's?