Mine isn't currently, but I'm working on it. The main complexity is that my wife and I share some passwords, and I want to make sure I do it properly so that transition is as smooth as possible. Vaultwarden is what you'd use to self-host.

But as others have said, I'm really not worried about it. Passwords are cached locally and only touch the server when syncing to the server. I want to self-host to protect against breaches, not because I'm worried about connectivity loss.

You can always backup your passwords (there's an export feature) if you're worried about it. I haven't done it, but I imagine it wouldn't be too hard to have a KeePass backup or something that you update manually every so often.