There doesn't seem to be any way of disconnecting a VE Pro instance, except from the controlling sequencer (or in my case, Sibelius) application. Deleting an instance which VE Pro thinks is still connected just results in an instruction to disconnect it first.
Which is fine, except when the host crashes or freezes. Even after rebooting my Sibelius machine, VE Pro thought it was still connected!
So I had no choice but to force it to crash and then reload everything, which takes forever. A "force disconnect" option on the server would have done the trick nicely. Just a thought.