Belichick is sticking around for more wins. If Vrabel is Head Coach and Belichick is Strategic Director or General Manager, then he doesn't get credit for coaching wins. Jonathan Kraft is President of the Pats, so I don't see that title going to BB.
Most likely, they lose Mayo if they go with Vrabel as HC. Kraft wants Vrabel, but I buy that he kind of fears having another of his legends moving on to, say, Sand Diego, and succeeding.