If your friend had 30 tanks and thousands of fish, they should have had a more involved backup plan that involved a dedicated generator in addition to a UPS. A small generator would have been a tiny fraction of the materials and livestock costs of running a setup like that.
Agreed though that it was a ticking time bomb. As for better backup plans: even autostart generators for data centers can fail when you need them most. Backup plans end up with more and more layers until you think you've got it all and then some little oversight will get you. In his case he probably could have done more but that's only because we're looking at it after the failure, for decades it worked.
Though the moment the UPSs hit 50% you might try to run to Home Depot and grab a generator, but by that time they'd all be sold out.