It would definitely be Minecraft which is been the most played games for years. It's community is huge and really adore this game and its idea.
it doesnt copy any other games it is very unique and has a lot of options to play on, servers of building, servers of PVP, servers of cities and more! I dont think it will die anysoon...
Probably minecraft as its been a big game since release. I can imagine the game still being active in 2 decades and I hope it stays as its one of my childhood games I played on.