Dive computers don't keep you alive during the dive, they keep you alive afterwards :P But seriously, if a dive computer fails, you go off your buddy's computer

Dive computers don't keep you alive during the dive, they keep you alive afterwards :P But seriously, if a dive computer fails, you go off your buddy's computer or scrub the dive and go with a maximum surface interval. At worst, this watch failing means you have to end early. Dive computers have extra safety precautions around surfacing too quickly, but divers are trained to use things such as watching air bubbles to time their surfacing. I have never seen a setup that only uses digital gauges for air pressure. This is all rec diving (<= 40m). I would never, ever use an Apple device for tech diving, even if some future version is rated for it.