Server usually fluctuates between 1000-2000. A lot of the old zones that used to be full are now completely abandoned (Dunes, Jungles, Qufim ect...) while you'll find high concentrations in places like Jeuno, any Aby zone, Gusgen, and Zeruhn ect...
Endgame Linkshells are still around, but the days of needing an entire alliance and competing against each other are pretty much over. Everything is mostly low-manned and a lot easier to do with a small group. Some events still need alliances worth such as Voidwatch, but there's constant shouts for those every hour.
It's never a bad idea to come back if you feel like playing this again. I felt the same way after 3 years and told myself to just give it a shot again, and I'm having a lot of fun now being able to do so much more content I once wasn't able with a couple of friends.
Watusa of Lakshmi
Same sorta thing with Watusa. I saw him fishing on the ferry one time. It felt like a hollywood celebrity sighting.