First off, the Phins would find it very difficult to trade to Buffalo that 2nd rounder they already gave to Philly. I think simply for the fact another team will be able to meet that offer the Dolphins lose the Travis Henry sweepstakes.
Arizona makes sense, but I'm also thinking Seattle might get henry. He fits with their needs, and will probably be cheaper than retaining Alexander. With Okeafor, Jones, and Hasselbeck also needing resigning, Alexander has to be let go, but on the other hand, they can't afford to go into the season with just Morris back there.