how can I delete users/PO/Domain without the server running the services?

A customer has quit working with an office and server & server connection isn't available any more - but I have to delete users, domain and postoffice.

If I delete users in C1 eDir users are deleted - but groupwise users get stuck because of agents aren't available.
Postoffice and domain I can't delete.

I couldn't find any solution yet.

Does anybody know what's to do?

Thanks for help,