Dynamix is no longer around. They have gone bankrupt (I believe, it was 1999 or 2000 that happened?)
The copyright age is 75 years from the date of the copyright.
However, I don't think it would matter too much if you sold it, for a few reasons:
1) The company is no longer around to enforce the copyright. (There is no one to represent the plaintiff, in the case that the copyright is found to be violated, and someone would have to find THAT out to begin with.)
2) Sierra (the publisher) doesn't really exist anymore.... it's merged with Vivendi Universal Games. (VUGames). I can bet no one at VUGames knows what Outpost 2 is. (To prove this, I once asked them a technical question about OP2. They were clueless what I was talking about and all they could point me to was the old OP1 knowledge base stuff.... basically a catalogue of how to get the OP1.5 updates, etc)
3) If you get the consent of the creator, you bypass all legal ramifications regarding the game. I highly doubt Dan Duncalf, the lead programmer and concept planner for the game would balk at the idea of releasing a sequel. (He'd probably welcome it, actually)
With that, I'm going to close this topic rather than run the risk of letting a full scale battle happen on the forums.