There are a few differing things at play in this situation.
Firstly, the MCL tear means surgery on the ACL will have to be put off for at least a month meaning it will likely be late January.
Secondly, coming back from an ACL tear is a lot harder for a big guy compared to someone like Peterson.
Thirdly, Gronk doesn't appear to be a quick healer based on what has happened throughout his career.
Really, I wouldn't be surprised if Gronk is forced to sit out next year because the Pats will have no option.
Say his target date to get back is the end of November next year. He will have to start on PUP and then be activated after week 6, meaning the Pats are basically wasting a roster spot for 6 weeks with the hopes Gronk can get back. Then he will have to work his way back into shape with the expectation he can help in the playoffs. That's a tough ask, both for the player and for the organisation. As far as I am aware the IR/designated to return cannot be used on someone who entered the season with an injury.
We likely won't know until April or May with how his rehab is going. If he can heal quickly he will play. If not, I don't see the upside for either Gronk or the Patriots.
BoneKrusher killing it with the sig