That is horribly cheesy and really stretching the bounds of believability.

Although the actor did mention something about a possible return, I highly doubt it will happen. Quaritch was the "villain", "Enemy", or "Antagonist" in this film, so naturally, they would have something else happen, rather than having the events of Avatar re-occur. I would still go see the sequel if Quaritch returns, but out with the old warhorse and in with a new problem, eh?

I'd say it's far more likely he will just play a different character (probably motion capture to avoid the obvious lookalike issue) if he is back at all (it was just something he said in an interview, which was nor official and has not been confirmed) - although I doubt he will be back at all, because Quaritch was one of the main antagonists and had an extremely important death - generally, recycling actors for something like that is bad.

As I said before though, reappearing in a movie/sequel in a different role is usually only done in irony or comedy. For example, the guy who plays the jerk doorman in Spider-Man 2 reappears in Spider-Man 3 as the slightly eccentric French restaurant host (comedy). Jason Isaacs in Peter Pan plays both Wendy's father, and Captain Hook (irony).

Yep, what Woodsprite said, pretty much.

Also, Cameron doesn't seem the kind of person to repeat actor-choices too often - I'm sure I've read somewhere that they ended up going with Stephen Lang because Cameron had already used Michael Biehn in Aliens and the Abyss as a serious, intense military guy, and three times would be too much.