Under US law (which applies to us; our servers are located in the US) the copyright doesn't expire for close to 120 years if I remember correctly. (This used to be 75 -- it got extended in the last few years). After this the work falls into the public domain.
In the case of using the word "OUTPOST," this falls under trademark law (which I don't know as much about, not that I ever claimed to be an expert on any of these subjects -- you'd have to ask a lawyer), as OUTPOST is a registered trademark, as well as a registered copyright.
Go to the USPTO website and search for serial number 74344515 (on some really crappy, hard to use system they have called TESS -- government websites -groan-). Before you think "oh great, registered August 9 1994" click on the TDR button at top (it's a series of blue buttons with text that doesn't line up) and notice that a picture of the Outpost 2 CD jacket was received by the USPTO on July 17, 2007. (Click on the "exhibit").
Interestingly enough, Cyberian Outpost, the owner company of Outpost.com before Frys Electronics bought it, brought a case against Sierra's Outpost trademark (there isn't much detail, click TTAB status at the top -- perhaps they wanted to "acquire" the Outpost trademark? I'm not certain how these things are carried out).
The copyright information can be accessed in a similar way. (Go to the US copyright office website). Search for registration number PA0000680808.
In any case this shows that the trademark / copyright is still legally defensible. It's not likely that any action would be taken but it's more likely if you are selling items that have the word Outpost in the name, in reference to the game. I'm not totally sure how well Outpost Universe would even fly on a tshirt (considering the content of our site, someone would have a hard time believing that the word Outpost isn't linked to the game).
As such I feel that OPU should not endorse any kind of OP2 merchandise. If someone wants to sell OP2 merchandise, they get to deal with the repercussions individually if Vivendi wants to take them to court for trademark infringement. OPU shouldn't be getting dragged into this.