Many years ago I was waiting for a Shuttle (a Trident!) flight at T1 and the staff were muttering about a computer failure. Then one of the said "we'll have to do it manually" and they started digging around in drawers only to be stopped in their tracks by someone calling "it's back". Huge sighs of relief and we went but a couple of minutes late.
I'm a little surprised there is no longer a manual backup capability.
On second thoughts maybe I'm not. These days, with electronic tickets if you can't access that ticket database how do you prove the passenger is booked and ticketed?