If the host account is not working and there was only one, you are in trouble. However if you have access to the database, you can turn any other user into a host user account. Just open the Users table, and put a -1 in the IsSuperUser column for a user account you know. Then the next time you log in to that account, you will have host level access again.

If you are using a shared host, you might not have access to the database directly like this yet. You can ask for it, or you might just ask the technical support to perform this record update for you once.