Well, good news. If you have a 75, you'll be 99 in under a week. Quicker if you dont mind doing a bunch of level caps in a row.
Also, once you're 99, you can solo Dynamis as well as Sky.
I looked earlier on my server, and there's 1700 people around. It differs a little from hour to hour, going up and going down, but there's still a solid playerbase playing the game that's going nowhere. Certainly not going to stop anytime soon, despite the doom-sayers that were upset due to someone taking away their items they could NPC for a crapload of gil.
All in all, returning to FF11 is better than returning to the steaming pile of dung that is FF14. So dust off your WS gear and come on back.