Invite wouldn't hurt. Though I doubt he'll be any good.
Problem is even if he was good at camp I doubt he would even be half decent for more then a couple dozen games and suck for the rest. In other words he would be using up a roster spot that could be filled by someone more useful and younger.
if he's does enough to convince whomever the GM is this summer that he wants back in the NHL badly and is healthy, I see no harm in letting come into camp on a tryout basis.
certainly wouldn't give him any guarantees, and he'd have to show not only the ability to still contribute, but also a positive mindset in being used in limited minutes (~15min/game) as a 3rd liner/PP specialist
If the Habs could "Radulov him", and bring him in for a post-trade deadline playoff series or two, it would be a lot of fun to see AK27 notch a classic slapper top shelf in the postseason, you know he would have a bit of magic in him, the kind of flair for the dramatic that could only happen in playoff hab land