There's still a strong community for Tribes, there's always a full server (as in enough people for it to be fun) or two for whatever mod (or base/classic) you want to play.
Tribes 2 does have a short singleplayer training campaign, plus you can play maps with bots if you want to. However, bots are never as good as other humans.
Most self-proclaimed "l33t" Tribes players though state that Tribes 1 is the better game, once you have a few client-side scripts to give it the Tribes 2 shortcuts.
Anyways, I'm sure most FS players/flightsimmers will like the fliers in T1 and especially the ones in T2.