I feel Simon is very much that cat in the eyes of COI and we are stuck there in that box of his. The list of times Simon could have and possibly had died is worth all of my digits. Radiation poisoning and later - burns, CO or CO2 poisoning (worth noting, while CO2 poisoning is rare in real world, this type of poisoning is still likely in Simon's scenario once he runs out of oxygen), decompression sickness (aka the bends), chugging rubbing alcohol, multiple blunt head and spine injuries, the list goes on and the severity is pretty steep for each of those alone.

In some way, Simon is dead the moment he's welded shut in the sub - this is his box and the timer is ticking, he could run out of oxygen without even leaving the dry dock.

The other time he could be dead is when COI lost contact with the rover once it becomes untethered in the second half of the movie, a lost speck in the endless blood. That is until he comes back within the radio range, even if Ava claims he was gone for days. Turns out this cat is still alive!

Upon each re-watch I was trying to guess which was the "this must have been it" moment, but Simon is just too stubborn to die, but also too fucked to live. His survival instinct is cranked to 11, he knows the odds are bigger than him by an order of cosmic magnitude.

And yet this cat still manages to claw his way out of the box and protect the black box with his life. And now the curse falls on what's left of humanity, the next Schrödinger's Cat.