I think that with Dorsey on board, we can pretty much guarantee that Matt Flynn will be here to "compete" for the starting spot. Mike Vick could be here as a free agent with ties to Andy Reid and then we'll probably see a draft pick in there as well as Cassel and Stanzi. I think you'll see Cassel as the #3 because the cap penalty may be too severe for an outright release. Stanzi could still be here to compete over the summer.
If this new regime is dead set on upgrading the QB position, I think we should expect an entire fleet of QBs on this team during OTAs and training camp.
I don't think there's anyway they keep Cassel as the number 3 guy. Think they would just rather eat the cap hit then have him filling a roster spot. If he's back he's number 2 at worst.