At this point seems that no one is either capable or interested in make an open world game to rival Skyrim. So if anything will make Skyrim obsolete will be the future TES VI. And that's if Bethesda doesn't mess up.
Considering their recent record... I hope that they go back on track.

Valheim is nice, but it's more a Viking Conan Exiles than Skyrim. Skyrim is another beast entirely.