You could absolutely rebase to Silverblue or Kinoite. Rebasing swaps out the core system files (basically, all the immutable stuff) and leaves /etc and /var untouched. So your home directory and other configs won't change.

However, Universal Blue is not likely to shut down, since there's many maintainers, and they have directions on how to create your own downstream distro, if you want. On top of that, BlueBuild has their own set of tools to roll your own distro downstream from the base Fedora Atomics.

So no matter what, the likelihood that you'll be stranded is almost zero.

ETA: let me know if you want more details.

https://docs.bazzite.gg/Installing_and_Managing_Software/Updates_Rollbacks_and_Rebasing/rebase_guide/

This should answer most, if not all of your questions.

It's important to remember, that you should rebase to the same DE to avoid issues. Although there shouldn't be any data loss when rebasing, a backup of your files is recommended.

Edit: Forgot to write, that these principles apply to all atomic distros. But depending on the distro you're using, the rebasing commands might be slightly different. So always look on the documentation of your distro.