If a big MMO closes that'd be rough, but those types of games tend to form communities anyways like Minecraft. You don't have to pay Microsoft a monthly rate to host a Java server for you and a few friends, you just have to have a little bit of IT knowledge and maybe a helper package to get you and your friends going. It's still a single binary, even if it doesn't run on a laptop well for larger settings.

With a big MMO, there will form support groups and turnkey scripts to get stuff working as well as it can be, and forums online for finding existing open community servers by people who have the hardware and knowledge to host a few dozen to a few hundred of their closest friends online.

Life finds a way.

If it's a complicated multi-node package where you need stuff to be split up better as gateway/world/area/instance, the community servers that will form may tend towards larger player groups, since the knowledge and resource to do that is more specific.