I would say minecraft, but... IS this because the world ended and you can only play the 1 you have installed, which means no modders are providing you with new mods, or is it because its some rule enforced on you by someone or yourself, so there are still modders out there that can and will update, and also the devs still updating the game?
I would probably quit games pretty fast if that was forced upon me, I'm not the kind of person to play a single game for many hours. I get bored in the middle of JRPGs and never finish them. I would probably choose the current multiplayer game my friends are playing and then later be sad as they move on to the next one.
The default answer here is Minecraft, there are just so much mods and easier to mod compare to Skyrim. Most games you will eventually know everything there is to know, thus become bored with it, especially with no or limited modding scene.
I feel like I would take Mount & Blade Warband, the game has great replayability, good mods and the battles are so fun that I don't think I would get bored