Is it safe to delete practitioners and clinics?

Hello.
I have a clinic with treatment rooms for different disciplines (massage, psychology, chiropractic…etc)
each managed with clinicoffice (each registered as different staff members working for different clinics).

1 of the practitioners has left our practice taking his “clinic” with him.

How do I safely remove him and his practice from Clinicoffice.
I would like to keep the historical appointments and payments that have already been taken in place, but remove the practitioner and clinic as an option when booking appts.

FYIO. I have already deleted this practitioner, and realised that his patients now have DELETED practitioner name on their records and cannot reinstate him because his username is already taken.