I have dealt with something similar but not exactly what your doing. Using Extended GAM i have found owners of events in specific calendars and then determined through AD if the users still were part of our organization buy creating a powershell report for that OU. Then i made a report for all the calendar events for specific Calendars what users were using which Calendar/Resource. Then i used a python script to compare the email address of the off-boarded users and the Calendar Events Report users. After that you then i was able to delete specific events for each Calendar/Resource based on the user name name and event ID.
If that will help let me know and i will pass on the steps to do that. BTW, i'm not a python scripter Ross Scroggs is the one that gave me the python script.