If your instance shuts down your posts will still be visible on the other servers that your instance was federating with. Which might raise concerns if you want to have them removed, but that's another issue.

On Mastodon it's possible to move from one instance to another, taking your followers and the list of people you follow along with you and having the old account point to the new one. In the threadiverse, the most important feature would probably be to not have to manually re-subscribe to a bunch of communities. I think this moving of accounts from one instance to another will probably become standardized at some point in the future, so that you could for example move an account from Mastodon to Lemmy if you should wish. It's probably pretty far down on the list of priorities though.

In my opinion, the idea of a hierarchy of users as enforced on Reddit through karma is a bit obsolete. I think we're posting and commenting out of interest in the topic or a willingness to help or entertain. If that's the motivation, I don't see how starting over on a different server is such a bad thing; you're not really losing anything. We're not here hoarding upvotes like a dragon hoards gold.