While I like Green I don't think I agree that he can't or wouldn't be cut if they sign Peppers. The Pats tend to play weird formations anyway, one or two linemen, etc and Peppers could always play D end as well as linebacker. I could very well see Jarvis being a casulty of this signing.
I think if they got Peppers, which is seeming more like a long shot (Shefter is almost always right), I dont see it affecting Jarvis. While the pat's do play crazy schemes, Jarvis is their top backup at the position (and Seymour hasnt been a rock of durability). Peppers doesnt want to play dline anymore, hence his demands for a trade where he can play lb. I dont think he would be happy with coming in and then playing a lot of snaps there. sure, I could see it a few snaps a game, but not as a primary backup.
Additionally, Jarvis's cap hit this year is: $5,406,720 (which is actually a bit high, but thats because he hit a bunch of incentives). The problem is, if they cut him, they would still have a cap hit of: $2,900,000. So you are looking at a cap savings of around 2.5 million. Jarvis is worth more then that amount in cap savings. To put that in perspective, they could cut Kevin Faulk (I am not suggesting they do that) and save 3.5 million in cap savings.