Steve Hernou - Personally, I would recommend hiding the name in AD if possible, over disabling the account. In fact, for sending purposes, you may not be able to disable it - our confirmation emails come FROM that address. So if the account is disabled, I'm not sure the calendar appointments would go out.
Plus, when our internal folks enter their email address wrong (sadly, it happens), then those 'failure' emails go back to that user account associated with the Bookings calendar (typically me). So, I've had to reach out to folks or just fix their email address on the appointment myself. Had I not seen the failure email get bounced back to me because it didn't match someone in our system, then our internal 'customer' wouldn't get a confirmation on their calendar AND they wouldn't show up for their appointment.
Again, if you can HIDE it from the address book in Outlook (so folks don't accidentally email it - yes, that's happened too), then I would recommend that. 🙂