The permanent status follows the account not the name. So the account that has all the posts and comments will stay permanent even if it is renamed.
If you look at your user info page there is a number next to your account. That is what the permanent account is attached to. Even if you rename that number stays the same.
If you look at your user info page there is a number next to your account. That is what the permanent account is attached to. Even if you rename that number stays the same.