To change details:
Saving does not email anyone. Players' offer pages and subscribed calendars show the new details, but the email they already got still has the old ones. If the date, time or place changed, tell the band with Email.
To call it off:
Every player who had an offer gets the email, whatever they answered. Their page and calendar show the gig as called off. There is no undo, so if it's back on, schedule it again.
Once a gig is called off, a Delete this gig button appears on its page. It asks first, then removes the gig, its offers, set list and pay record. Nobody is emailed.