Revis Contract is the biggest burden out of anything, he isn't doing to renegotiate that thing, nor would he, he could probably get a similar deal from some dumb team out there once he gets cut.
The only way the Patriots get Revis is if he takes something like 12 Million per year with huge guaranteed money for a long time (and even then it because he chooses the Patriots over some other garbage team), but then of course the Patriots are on the hook for almost the entire contract whether he sucks or not, and coming off an ACL, who knows what the future holds.
The Patriots never like going all-in on a player and thats exactly what this potential deal would be, They have been burned before on contracts like this (Adallus Thomas) and like to have control over players they develop in their own system by handing out deals when it is good for the team.
There is no way to win this situation they find themselves in.
If the Patriots trade for Revis, they pay close to (or actually) 16 Million Dollars for a single player, who if god forbid he gets injured or something play up to his contract, would have cost you potentially 4-5 discount quality players who always seem to hit or miss real hard, you can kiss any chance of signing Edelman goodbye and you also put impeding free agents of your own at risk in the coming years since Revis will never renegotiate.
If the Patriots don't end up with Revis, their secondary will be as horrible as it has always been without a star db; Dennard, Arrington, Ryan are nice little players, but they arent going to be worth a damn without a star db amongst them. This is a passing league and the Broncos will put up points at will if you are lucky enough to meet them in the postseason.
Damned if you do, Damned if you don't.