It was already over by his last season. The 2018 post Super Bowl contract showed you that the split was about to happen regardless. He himself was on Ross's boat. The team was old. Yes, they could've kept him and signed him again in 2020, I would've preferred that, but the team, as old as it was, needed to rebuild, and he was looking for a championship situation. That window had closed for him for the next 2-3 yrs if he stayed on in New England, given the massive personnel losses into retirement. I cheered for him that year. Both sides decided it was time after the 2018 season.