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.
I've been on and off mastodon since 2019 and I've really wanted to like it, however the lack of a usable search kills it for me. I guess when your the main dev and you have half of mastodon following you a usable search isn't really necessary. Someone did try to work on a way to scrape and make mastodon searchable but they got hounded off mastodon I believe?
I tried to use hashtags but the ones I followed seemed to have a large number of terminally online/bots posting links making finding anything useful practically useless. In the end I got fed up of the feeling I was shouting into the void. I want to use and like Mastodon but I felt like I was fighting the system.
I'm just glad Lemmy seems to have taken off it's not perfect but it's certainly on the way