GigSpace chases your acts so you don't have to. Each booked act is asked to re-confirm in the week before the gig, and again on the day.
The week check-in is a heads-up, not a deadline: an act who skips it is still booked, the gig is not marked at risk, and they're asked again on the day. The day check-in is the one that counts. If an act doesn't confirm on the day, you're told and the gig shows as at risk. If they still don't, GigSpace can cancel the booking and offer the gig to your backups automatically.
Nudging an act. Open the gig on the Booking Calendar: the Check-ins box says where each one stands. While the act still has one to confirm, Nudge to confirm sends them a reminder in GigSpace (a push, an email and a notice). One nudge a gig a day. Acts who aren't on GigSpace yet can't be nudged: call them.
The day-of alert, a gig today with nobody confirmed, is the one notification that can't be muted. It's the last line before a venue is left short.
You can see the confirmation state on every upcoming gig, so the Friday-morning question of "who's actually turning up tonight" has an answer on one screen.