I don't think it's about salary cap.
Even if he once was, maybe still is, the fastest guy in the NHL, last year was the first year since 2002/03 that he got close to playing a full season. Seems to get injured a lot. That's too much of a risk for Gainey.
In anycase, Montreal has plenty of prospects at soon to be NHL skill levels, remember they gave the Leafs Grabovski which ultimately allowed them to get Lang. Grab played about 20 games for the Habs last year, and the Leafs have him playing full shifts thus far.
If Tanguay plays above average (good start so far) this year they'll try to sign him to balance Koivu's not French speaking ways.
Higgins, he was rumoured at the end of 07/08 in the package for Hossa, so Yah, he can go, sorta.
Unless Gainey is desperate and doesn't think his team can make it to the top, then maybe he'll make a play for Gaborik, but as long as Price / Halak play well I don't see it happening.
JZ