I remember a lot of hubbub about retired healthcare staff being brought back, but I also remember there being a lot of talk about them willing to go back but not actually being needed/getting stuck doing online training courses about radicalisation before going back onto the front line. It struck me very much as an optics story, but not one that materially made a difference
A driver could probably prove competence relatively easily, but it's having the system for them to prove their competence in place that would be the trickier part. Plus of course, it's not just the drivers, but maintenance staff (if they can catch a break between inspecting welds), guards, platform staff, etc.
If push came to shove then I'm sure they could reintroduce HSTs from a competency/training aspect, but the situation would have to get pretty dire for that to be the case
As for the stock itself - per
this post only 5 ex-LNER sets made it into traffic with EMR, 3 of which are still in traffic (for 2 diagrams) with the other 2 sets stored at Ely & Neville Hill. The Neville Hill set was due to move to Ely but I suspect they might hold tight on it for now! From next weekend all 5 sets would be available to press into service (assuming that they aren't also being ran into the ground) which does make it feel like it'd have to be a real "last roll of the dice" to consider their introduction
Oh, it's definitely the least of the issues, but between the (some would argue rightful) pig-headedness of the DfT on the matter of PRM-TSI, the poor-optics, and the fact that we've still got a zombie industry being propped up by Westminster which is generally advising people not to travel, it won't be the first option they turn to