I am new to Tremulous, but here is my two cents as someone who has played Natural Selection for 10 years and witnesses it's death (as well as numerous HL1 mods). It's natural for FPS games to dwindle in population as time goes on, it seems that the length of survival for newer games is much shorter these days than for old games though (Tremulous, Doom, Mount&Blade,Counter-Strike, etc). NS has been dead for almost a year now, a few servers but no one plays anymore, and it has a sequel but very few play maybe 1000 at most. What I wanted to say is that I think tremulous has lasted a long time and will probably last a lot more, but the longer it goes depends on how strong the community is, once main communities die then people stop playing and they move onto other games as it splits. Mount&Blade mostly survives because there is huge community and many events for players, Doom and Tremulous people still play because of the gameplay obviously. I think best thing you can do to keep game alive is be nice to noobies and foster a good community. A updated sequel that's structured similarly to original game and daily updates are what keep game community alive in future I think.
