The GP didn’t mean “wait 5 minutes before making any action”, they meant “stage the change so the user can see the result of their action but they still has a grace period to undo it”.
I’m not saying there isn’t a better way Github could handle this situation. Just that I do sympathise with the decision to cascade delete.
Stop sending notifications to watchers, and replace the repo in the stargazer's starred list with a "The following starred repos are currently private and cannot be viewed:" and make the stars be remove-only for a while.