Well, I guess that just leaves us with either a pair of 37/4s, or Deltic haulage now then
Time to look forward, not back. The options as I see them for FGW (plenty of blue-sky thinking here):
1) Status quo, with FGW using their 57/6's with hire-in 57/3's as required (doesn't have to be DRS....)
2) FGW sell their 57/6's (to a ROSCO?) and lease in all locos - be that 57/3 or /6, 67, 68 etc.
3) Once the GW line is electrified, 90's or 92's can be used for the electrified part of the route (in a similar manner to the Caledonian Sleeper) with diesels for the remainder.
4) Purchase / lease bi-mode locos (although Class 88's might be short of power in diesel mode)
5) Form a micro-fleet of converted HST power cars, once cascaded by IEP, to top-and-tail suitable for use with Mk3 stock (i.e. loco electrical system changes).
6) FGW procure generator cars (either as carriages or converted Mk 3 DVTs) for each set and can then use pretty much anything to haul the trains.
7) Procure new trains (long term).
Using stock even older than the 57's is not a credible solution. How hard can it be to find 4 reliable locos??!!