All alerts - both scheduled as well as real-time - get resolved when the alert process run at 3am local time each morning.
Scheduled alerts check to see if the alert in question is still outstanding. Is the issue causing the alert is still active nothing happens. However when the alert is no longer outstanding either because the alert was turned off, the settings changed or the data changed causing the issue to no longer be active the alert will be resolved.
Real-time Alerts (Unwanted Person)
All real-time alerts will clear the next morning.
For more information on the difference between the scheduled vs real-time alerts see: How alerts get created
And for more information on viewing alerts see: How to view alerts