3M is fine for a dependable player like Evans. It's not 2013 anymore, the cap has raised and will do so again sooner than later.
Saw another one of your comments which was about the Habs needing to get to the building phase. Well, he's far from a core building block, but when you have such a dynamic defensive forward who you can consistently count on, it's worth something. Especially at center. 3M salary for a few years will not be the reason why they can't afford something else. Dogshit players like Anderson, Dvorak will be though, inflated contracts like Gallagher, Armia also. With that sad roster, if a generous but fair contract to Evans is what makes your long-term plan crumble, you're in big trouble.
We don't even know if Beck or anyone else in the system will be as reliable as Evans (excellent checker with faceoff ability). The team sucks ass in most defensive metrics and in a situation that somehow couldnt possibly have been foreseen, the youngsters are actually in over their heads or just surviving, and the vets arent leading by example with constant blunders. Evans is one of the "vets" who actually show the way. Hell, I'd take a 3rd line with all Evans clones at the 3 forward positions if I could, it would probably be one of the best defensive lines in the league.