If the sleeper roster is a very small part for the Scotrail drivers then there isn't really an issue there as the drivers will just be re-rostered to cover the day trains. The worrying parts are for the drivers whose rosters are almost all sleeper work, i.e the Inverness DBS crew who don't have much else up here. Are they to be TUPE'd over to the new traction provider? More worryingly as far as I am concerned, are the arrangements that will have to be put in place for the depot. There will be a need to share the space with what could and probably will be, two separate companies who will be requiring pit time in a shed that's already too small for the work currently being carried out. I personally think that the cyclic maintenance will be removed from Inverness to either Polmadie or Wembley, but the sleeper will still need cleaned and prepped. I can't see permission for the set to be left in Platform 1 all day, so the coaches will require shunting to another area to be serviced.
I think the delay in announcing the forward plans are more to do with these kind of problems rather than waiting to see if the next Scotrail franchisee can run the sleeper for Serco or not. This is the reason why the all of the depot staff are on edge, not just the staff who will be TUPE'd to the Sleeper side of the business.