I'm afraid there's no easy way to do this, it will require custom scripts/database queries to move everything back to the appropriate tables and this can be a significant amount of work. Even for small forums/databases.
See why everyone is turning away from vbulletin lately? Due to small instances like this that add up over time. Impex needs to be updated & modern. Simply no excuse not to when other companies keep their converters up to date. The only reasonable & acceptable excuse not to update it would be laziness.