Yes, I would be surprised if this happens this season. First of all I don't think Mourinho is in the right state of mind right now to jump into another big job (he may think otherwise, but someone should know better – his last few months at Chelsea have been nothing but a total emotional meltdown) and besides, it would look very weird for all parties if an iconic manager of one big club takes over one of its rivals mid-season. Plus there is the issue of Mata and any other current United players Mourinho may not like – it would be stupid to invite him unless you're prepared to do major surgery on the squad, which is impossible to do mid-season anyway.
All in all, if LVG is fired, I would expect Giggs to be given a chance until the end of the season.