One account should be deleted before linking two existing ones

I'm trying to replicate the example of merging two existing accounts, but I think that the problem is that the docs doesn't explicit says that the `prevUser` needs to be deleted from Firebase Auth, and not only its data from my "repo", it just says that I need to delete the users's data:

https://github.com/firebase/snippets-web/blob/88aa8eb8210c90263eef7fe1f454cd6477a5a252/snippets/auth-next/link-multiple-accounts/auth_merge_accounts.js#L21-L22

And it says that it would be restored if necessary, but it doesn't restore the actual user that should be deleted beforehand. But to restore it we would need the `prevUser` credential, that wouldn't be valid anymore?! Idk...