What if Bill Belichick really did leave the Patriots in 2018?
How would this have changed the NFL?
Where could he have gone?
The Belichick vs. Brady rift would have ended abruptly with the departure of the former instead of the latter (I think the Bucs will be a big loser of this alternate timeline)
Leaves a massive change for the Patriots in terms of just a different atmosphere. No Belichick would probably cause Kraft to return to splitting the HC and GM positions back to two separate people to work with. I would concur with Alt in McDaniels taking the job (most veteran member of the staff and someone Brady relies on) and Caserio probably takes up the GM post, given his ten years as player personnel director. What happens to the Texans after that is anyone's guess.
As for Bill Sidious (only jokingly; mostly roast Boston sports as a playful jab with my old man), the Giants seem like the likely option out of the simple fact that the now-WFT would have too much upstairs involvement in Snyder (even if he could work with Alex Smith as a QB option) and the Dolphins, while possible in order to rid of Adam Gase, sounds like there would be some sort of "clause claim" similar to the Patriots to Jets in 1997, then the Jets to Patriots in 2000 (not to mention Gettleman is automatically out as GM if Bill convinces ownership enough on that option). Given the OTL record of the Patriots, I wouldn't be surprised if Belichick picked Saquan as OTL, if not trading down for picks and picking up O-line pieces for Manning and also getting Chubb instead. Granted, with the options of QB, Belichick could look at benching Manning in hopes of developing a successor (there was Etling in the seventh in OTL, and also Teddy Bridgewater in the FA market before the Jets picked him up and later traded him to the Dome, and, with the pick being high enough, Darnold, Allen, and Jackson are all there).
Overall, if McDaniels and Caserio manage a sweep in getting Brady a bunch of pieces alongside Gronk and Edelman, I could see both teams having a benefit with the Giants having an outsider's shot at going to the playoffs (potential sendoff for Eli) and the two teams ending up as potential SB contenders (provided the Giants can get through the Rams and Saints and the new look Patriots can overcome the Chiefs).