A new PowerShell command has been made available on Exchange Online only.

This command allows you to cancel all future events (meetings) for a mailbox (user or resource).

This will automatically cancel the invitation to all attendees; this can be quite helpful when somebody leaves the company and did not cancel the meetings (especially the recurring ones).

You can go to https://technet.microsoft.com/library/mt784593.aspx to learn more about the command

Enjoy