All of this should be covered by home and contents insurance. If he doesn’t have that, it’s his problem.
Regarding the notification, it’s hard to see how anyone could be expected to know that there were problems with his unit that weren’t replicated in others. Again, if he doesn’t have a friend in the building or nearby, that’s his problem too.
I would be as sympathetic as possible and maybe offer to hold a key for him (so people can get access if there’s anything similar in the future). But are you liable? I doubt it. And there’s nothing I can think of in the Act that even refers to such an eventuality.
The only thing would be if the electricity to his unit was permanently disconnected … but it wasn’t. It was only inside the unit that it was shut off.
You could run it past your strata insurers – you never know, they might cover it – but if they’re not on board, pass it straight back to the owner. If he couldn’t foresee a situation like this, and take suitable precautions, how can he expect you to?