The Aldwych unit is maintained to some kind of schedule so should be in something approaching reasonable condition, and it has the benefit of having spent something like 18 out of its 45 year life under cover and not doing very much.
Nonetheless I still think the boat has sailed as regards using 67 or 72 stock. Yes it would be possible to make up two four-car units, one using the Aldwych unit and the other from the AIT (assuming LU want to give either unit away of course) but that doesn’t make for a particularly flexible fleet, and it would require 100% availability. Unless there are some cars sitting around off the radar, my understanding is something between most and nearly all other spare cars have now been scrapped, in some cases very recently.
Making 72 stock into 2-cars would be expensive, and the reason the MAs went on the trailers in the first place was due to lack of room in the motor cars. So it’s necessary to move both MAs and compressors to the motor cars. Then for any length it’s necessary to modify to third rail, then get the cars to a standard where they are considered acceptable to passengers (remember they are still in largely as-built state) and where their performance will be reliable. As a compromise it might be possible to more viably reduce to 3 cars, but two units still is’t enough, and 3 cars is a reduction in capacity compared to potentially 4 today on the busiest days.
A lot depends on how urgent it is to replace the 38 stock, and no one seems to definitely know the answer to that. If the 38 stock physically cannot be kept going then something will have to happen. Otherwise I can’t see anything other than status quo. There’s no point in replacing just so someone can say we now have newer (or less old!) trains if it means there is less slack in the fleet, so worse reliability and less chance of long trains on the busiest days. From a perception point of view I’m not sure unrefurbished 72 stock would appear much newer than 38 stock, plus they perform worse in poor adhesion!
Unless something from abroad is in the offing, my money is on the existing trains continuing, perhaps with another unit withdrawn for spares. Time will tell...