When MMOs shut down they should release enough material that fans could run their own servers. I see there are some threads on the web talking about "Dungeon Runners Reborn" and how some fans are trying to create a server. It's great when those don't get lawyer'd out of existence and some old fans can try it again if they still care enough. Those tend to be slow to develop and have no shortage of bugs, but when it finally works that can be a lot of fun.
I played MMOs in the early 2000s, and that has probably biased me against extremely-online games: knowing what happens when they decide it's not profitable enough to keep a service running. "Press F to erase the realm."