A pair of 86s will always be superior to a 90. 90s can't be re-geared (downwards) so options are limited.
The 92s are a conundrum. They have massive hauling capacity, will haul 1600t uphill and down dale at their design speed. They'll do more than that too. However, they are massively complex due to the chunnel working requirements.
A 92 can be readily overhauled, Brush have a package to enable this. I'd expect more 92s to be returned to service. DBS are less likely to want to sell these as there are other operators who would take them without doubt.
All of these 90s have been robbed, some butchered in the process. Anyone considering purchasing for overhaul would have to be looking at anything up to the half million to return to service. Also bear in mind there are no spares, little is common with other classes. Asking Alstom to manafacture small quantity of anything is going to be seriously expensive. Anything obsolete may mean that approval work is required further pushing up the price. In all honesty the only place I can see work is abroad where they can manage the overhaul process more cheaply (cheaper labour). Failing that, assuming they sell, I'd imagine the cutters torch awaits.