First Off, football speaking bringing in Peppers is a great move. He can stand-up or play DE. Exactly the type of playmaker that this defense is sorely lacking.
Now, as for the business aspect of what is going to happen to him, that is much more interesting...
Carolina certianly can not Franchise him AND KEEP HIM, his salary, even in an uncapped year ($21 MILLION) would be too much.
Carolina could Franchise him and then work out a sign and trade deal with another team. This becomes much more likely if we go into an uncapped year, because it brings back to the table 8 teams who otherwise would not be able to bid for Peppers, due to the "Final 8" restirctions on signing Free Agents. It is a bit of a gamble for Carolina, because these teams that are limited in signing free agents are not going to be as cavalier with trading away draft picks, as they would be if they were not restricted in the amount of Free Agents you can sign.
The problem with this for Carolina is, that if I'm Peppers, I sign the Franchise tender the minute they issue it, locking in the 21 MILLION DOLLARS (said with right pinky finger on side of mouth). Then Carolina is stuck (if he didn't sign the tender they could recind it later on and he reverts to being a Free Agent), they would have to deal Peppers then, and whoever they deal him to would have to first work out a contract re-negotiaition. That is alot of ifs and buts.
IF Carolina goes the Franchise and trade route, I say the Pats wait it out.
Carolina is going to get a 3rd round (comp) draft pick next year for Peppers, so they would have to think that they could score much higher than that in a trade in order to risk Frachising him again.
IF he becomes a UFA, then the Pats are in the drivier's seat, because the Cowboys, Jets, Chargers, Colts, Vikings, Saints, Baltimore, and the Cardinals are all out of the running. Anytime Jerry Jones and Woody are on the sidelines, the price is bound to go down. Plus it leaves that Pats as one of the few true SB contenders he could sign with. So I really don't think the contract will be that outragous.