This is, of course, a big loss, but the Patriots will be fine. They have played most of the season without him and as long at Brady stays healthy this team will always be in it.
This is probably a bigger hit to the fantasy owners that have Gronk. Probably spent a 1st or 2nd round pick on him, and outside of that 4 game stretch in weeks 5-8 he either hasnt played or was basically a decoy while nursing another injury.
The bigger question I think becomes is this the beginning of the end for Gronk in New England. Bart Scott said it earlier today, and I cant say I totally disagree with some of the things he said. Eventually these injuries will catch up.
That said, Gronk could be back just in time for the Super Bowl. If the Pats make it there AND can add a well rested Gronk, whoever they are playing has NO chance.