If keep JG, here's the problem. If Jimmy stays and Brady maintains his excellence (which is likely), you've lost tons of leverage in trading him. Every te yam knows that the Pats would have to franchise him, and I have no idea if that's even going to be possible, but lets say you can. Like in 2009, franchising him only gains you a few days to make a trade because having Brady at his cap number and Garapolo at over 20MM would completely paralyse any FA activity UNTIL you make that trade.
So every team KNOWS that you have to move fast. The ONLY reason for them to trade anything in the first place is to eliminate the risk of having to recruit him. The whole league knows you eventualy have to drop the franchise tag. So JG loses value because the time considerations. Then there is the money. Anyone who wants to trade for JG next season knows they also have to pay him at LEAST Ostweiler money from day one, if they get him this season they get a year to decide whether to play him big money. So that loses you value in the market.
Unlike this season, Jimmy is likely to get very limited snaps in his last year with the Pats, and his 6 great quarters in 2016 will start to fade over 2017, and that CAN'T help his value. Finally the QB draft class THIS season flat out sucks. There are no QB's worthy of a top 5 pick. Hell, I just read where on draft guru at NFL.com doesn't believe there is a single QB who is worthy of ANY first round pick, and NONE look to be an immediate starter. But there is no guarantee how the 2018 QB class will look, except it almost has to be better, and THAT would lower JG's value if it's a better class than this one. Bottom line, under those circumstances, the Pats getting a midround 2nd rounder would be a great job by them, and the more likely result would be a 3rd.
I personally believe JG is worth a top 15 pick this season and a 2nd day pick the year after. There is only one FA QB prospect better than JG, and that's Tony Romo. So if you don't want to spend big bucks for a good, injury prone QB at the end of his career, JG is hands down the best QB prospect any team who needs a QB can get. No one in the draft, no one in FA, no one you can trade for.
So if you believe that, and gi ven how important having a good QB is to the success of a football program, how can you NOT give the Pats your first round pick. We all know how even first round picks are crapshoots anyway, JG is a MUCH safer bet, at a much lower cost. How can you not make that trade.