Oddly enough, I made your exact same argument many times this offseason, but I don't expect every single penny to be carried over. Either way, let's say you're right and they have that much money available. It still doesn't address the 2 biggest issues in terms of Garoppolo choosing to stay here as a backup instead of going somewhere and starting, and it doesn't address what to do with Tom Brady.
Well, it's just short of $27M right now and they have yet to address reducing Amendola's $7M cap hit down to a reasonable number (say, $2.5M). And, again, what other major expenses might be coming? Draft picks will be about 1/2 million. NLTBE incentives that are earned may ultimately deduct 1-2 millon.
So, it's not a question of "every single penny" being carried over. The question is whether or not the ultimate carryover number will be
substantially less than $27M.
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If there really is
only the possibility that one of the two
must be a full time backup for the entire season and the other the full time starter, then the Pats will need to "read the tea leaves" at the end of this season. At that point, it seems like it's down to either franchise and trade JG, or franchise and keep him around for another season of leaf-reading, whether he likes it or not (for his $20-something-million guaranteed paycheck).
The only alternatives I can see are (barring catastrophic injury to Brady or significant, obvious decline):
1) Brady has already set a career end-date that we don't know about and JG is already scheduled to take over at that time.
2) Some sort of rotation that provides JG with more starting experience (and reputation/potential trade-value enhancement), and provides Brady with enough relief/rest during the season to keep him playing at an elite level longer.
The only way #2 happens is if Brady, JG, BB, McD, and the Krafts are all on board. Since we can only speculate about what they're all thinking, it's as possible as anything else.