Brady passed for like 505 yards in the Super Bowl, and that is without Julian Edelman. The sky is not falling. I would just fix the defense and they are good to go.
This may be an unpopular opinion, but I think the answer is no one has any fucking clue.
We may look back in two years and say, in hindsight, this was "peak Pats". Or we may look back and see them as champs a year from now, with this same offense getting a different result.
Right now, no one knows. Brady was still at the top of his game in this Super Bowl. Gronk was still Gronk. Hoodie had his top assistants.
Some of those things definitely will change, obviously with Patricia and McDaniels moving on. But Belichick has overcome this before. Gronk is making noise about possible retirement but I think he comes back at least one year. Edelman will return as noted, and Cooks and Hogan and others will be there. The offense will still be good.
On the defensive side, the Pats have a lot of question marks. They were bad this year, and it is hard to see them immediately getting better. Butler is about to walk, and they don't seem to have much young talent coming up.