They are never getting the draft pick back. The NFL would rather piss off one team than 31 teams. Kraft & TB could get money back and certainly a massive cornerstone of any potential Brady defamation suit.
But I don't think in the history of the big four sports any team that has lost a draft pick in year N-1 is found "innocent" later on and is refunded the pick in year N or N+1. Just doesn't happen.
Seriously. If there was video footage that surfaced tracking McNally walking from the officials' office down inside the bathroom, then on to the field, and it showed absolutely NO tampering with footballs, the NFL *still* wouldn't apologize or give the Patriots' picks back. In other words, even definitive proof shown to the entire world still wouldn't do this, because Goodell would simply say, well, he destroyed his phone and article 46 and whatever.