As long as lemmy remains popular there will be new servers/instances popping up. I found my start on lemmy quite rocky with servers vanishing sometimes with notice and then others just vanishing without notice, Anyway I quickly adapted and began to keep a list of communities I like to frequent while this list is still small I’m sure by the time it starts to become an issue there will be tools that make it a non issue.
I’ve started becoming more nomad in my use of lemmy compared to somewhere like reddit where I had just one account for eight years I just open a new account with the knowledge that it’s not permanent it doesn’t belong to me and there will be a time when I need to move on.