LVG lowered his target some time ago by saying that he'd won a trophy in every Country he'd managed in... while talking about the FA Cup. So if we win on Saturday, he would be able to leave with relative grace, his 'trophy' record intact.
I think the stay or go decision would have been made some time ago, and if he goes United would I am sure issue a "thanks for what you've done to start the rebuilding and for the trophy, but we now have to plan longer term, end uncertainty, and make the change" statement.
If we fail to win the cup, things will become a bit more messy though, whether he stays or goes.