I find it incredibly hard to believe that there is no succession plan for Brady, whether it involves Garoppolo or any other QB. If Brady is playing at an MVP level and the team is winning SB's, cutting or trading him is just crazy talk. I just don't see BB "winging it" in this area, throwing his arms up in the air and not having any idea of what to do.
Essentially, there are basically three outcomes: Brady decides he has had a fulfilling career and retires (most likely after winning another SB), Brady suffers a serious injury and doesn't come back the same, or his production takes a serious hit do to declining skills and age.
The first one seems like the most likely outcome IMO. If he wins a 6th title, he will be on a mantle no one else is close to getting to. The second option is always a possibility, which IMO ties in to Option #1 . . . get out before you suffer a potentially life changing injury.
Option #3 is where the potential awkwardness comes into play. If Brady is no longer producing and costing the Patriots wins, then the team would have to evaluate benching him, trading him, or cutting him. Brady playing in another team's uniform would not be a good look for NE. There is no reason for Brady to have to find a new home in his forties.
As discussed ad naseum in the Garoppolo thread, it becomes a financial burden to keep two QB's beyond this season and pay them both starting QB money. The simple solution would be to franchise JG for next year, but at that point NE would committing to a $22 million cap hit for Brady and likely another $23 million for Garoppolo. While I suppose it's feasible to do that, tying up $45 million of cap space to one position is not a good business practice, especially when only one of the two could be on the field at the same time.
If the Patriots are ready to anoint Garoppolo as Brady successor, than it would be in their best interest to negotiate an extension with Garoppolo with some sort of tiered salary scale. For example, they could give him a 5 year extension with a $6 million salary for 2018 and $18 million a year thereafter (so 5 years, $78 million). That would translate to Brady being the starter in 2017 and 2018 and Jimmy G. taking over in 2019.
I can see BB letting things play out for one more season (2017) to see what happens in the interim. Brady could get hurt. Garoppolo could be forced to play and could bomb (meaning that maybe he isn't "the guy"), Brady's play could drop off, Goodell could suspend Brady for a season for calling an illegal audible, Brady could win another title and retire, etc.
If the plan is to potentially franchise Garoppolo, I don't think it is a coincidence that the Pats have $20 million in cap room left and haven't really done anything to spent it. They have a couple of mid round rookies to sign, but their roster is pretty close to being set. Maybe they will go out and sign someone like Revis or McCourty, but it doesn't look like they are looking to make a big splash at this point. The point being, BB may be able to pay most of the cost to franchise Garoppolo NEXT year from THIS year's salary cap money. If that is the case, than double paying for a QB in 2018 would become more feasible.
That still could only be a temporary fix, as Brady could want to play more than 2 seasons and Garoppolo is going to want to both play and get paid. As I said in the other thread, there could very well be a plan or agreement already in place known only to Brady, BB, the two Krafts, and Don Yee (agent for both TB12 and JG).
When it comes to what to do with Brady in the future, I am not sure BB has 100% say in the matter. The Krafts likely have veto power, and I am not sure they would let BB cut or trade Brady. Without knowing the circumstances it would be hard to tell if the Krafts would sign off on it, but I do think they would initially vote against Brady playing elsewhere.