As much as we want it to happen, the Pats don't really have the cap room to invest $15M in two players and expect to improve in other areas. That's why I don't think the franchise tag on anybody is a good move. If they're going to sign a Talib type of player this offseason, then they really could use the low first year cap hit (say $6M on an $8M a year contract) rather than the $10M for one year.
I agree with your approach, but that's also assuming that those 2 players are going to have cap hits of 7.5 million dollars too. That most likely wouldn't be the case in my opinion, as I think it could very well be lower for a year one hit unless we're talking about bringing in some kind of major mega-signing(s).
I highly doubt that even Welker and Talib would have a combined cap hit of 15 million dollars. Even though I am assuming that both of them will be gone, you could use those kinds of players for an example. I would think that Welker's aav wouldn't be much above 8--8.5, let alone his cap hit for year one. Talib's aav probably wouldn't be much above 7 million at the max, so he wouldn't approach that number either.
Regardless, I see where you're going and I agree with you that they'll have to be cautious of the level of player that they run out and sign or re-sign. I also think that it will end up being just fine though, but that's just my gut.
Personally, I am starting to think that the high likelihood of seeing a Brady extension may actually end up being more for the draftees or even carried over cap room again. I'm starting to think that they'll be just fine as far as it comes to the salary cap, but then again I am also preparing myself for the departure of Welker.
If Talib stays it won't be on a mega blockbuster deal in my opinion, so I think that they could very well re-sign a couple/few of our lesser cost players along with competing for at least a few middle tiered FA acquisitions without much problem.
I think if Belichick feels there is concern then we'll see Brady extended earlier in the league year, sometime after the March 4th deadline for tags which would take the highest average of the 5 top QB's. I don't think anyone will do Baltimore any favors by restructuring or extending before then. If Belichick doesn't feel that it's that much of a concern, then the Brady extension won't come until sometime down the road into the later spring or summer when they think they'll need it.