The Raiders aren't going to fire Josh McDaniels... Unless things go totally tits up, he's there for the duration of the contract... Mark Davis is the poorest owner in the NFL... the most widely reported net worth of Mark Davis is in the range ≈ 500-700m (outside of the team valuation)... one report indicated he's worth 1.9b, but who knows... while thats a ton of money, its not enough to swallow ≃ 15-20 million a year in dead money for coaches (McDaniels & Gruden) plus whatever you need to pay a new coach...
If for some reason the Raiders get an infusion of cash, ie Mark Davis selling 49% of the team for ≈3 billion dollars and they do let them go, I would take him back here as an OC in a heartbeat...
If they are serious about bringing BoB back, provided he agrees to a minimum 2 year commitment, maybe the timing works out if McD is let go at the end of his run in LV... but thats highly speculative conjecture at this time... who's to say BB will be here at that point and time... the team could be going in a completely new direction...
But i don't see either scenario happening... I do believe McDaniels time in New England is over.