Having known Martin and dived with him, this is truly sad news for me. He was very fit and an active diver, so cannot see any fitness issues related causing this.
I've never seen, dived or enquired about the Pathfinder, so would be interested to know:
1. Does it have water activation / deactivation sensors
2. Are there any audio or haptic alarm systems
3. How visible the HUD is in shallow water
4. Is there any redundant battery supply
Sad for me to say, but perhaps floating above his kids, enjoying watching them learning to dive, he wasn't keeping his eye on his unit (hands up, I probably wouldn't be either if I was watching), and any number of things has happened to cause the unit to stop working (we can say this due to the lack of dive logging), be it battery failure? too shallow to cause system to shut off? then the next question would be, was there any alarms that should of alerted him, even if he was not paying attention to his handset.