Hey Mark,
Got an update for you: We have nothing setup to revert back to a non-tenant account. If the client wanted this done it would be very manual with a good chance for error. We also need to consider what would happen to customizations, since in a regular account tenantid is 1 for everything, but you could have setup a customization with something like tenantid in(2,3, etc.) which would then show nothing.
A suggestion would be to remove the tenants and all tenant related customization, then use the head office as the main account. There is no harm in having a multi-tenant database vs. a single tenant one, it just has more muscle.
- Ashur