Of course volunteers call in sick, go on vacation, or quit altogether. Rather than deleting each individual assignment, VSys gives you two links on the person's Assignments panel: Cancel for time period and Cancel all.
Clicking Cancel for time period prompts you for the date range for which the assignments should be cancelled. All assignments on or between these dates, including those within a recurring assignment, will be marked as "Cancelled by staff member".
Recurring assignment schedules are not affected, only the actual assignments within them.
Cancel all cancels all of this person's assignments from the current date forward. All assignments are cancelled, including the recurring assignments themselves.