Wouldn't be surprised to find Bart Torgal alive in Subnautica 2. If the cinematic trailer for Subnautica is canon - he left the 500 meter base and built a seamoth and a research base to study the sea creatures (I'm 50/50 on whether he went to the island to die after or before and realized his message was premature - we never see a dead body of anyone in this series*). The reason why we didn't find this base and its location is implied in the trailer. * There are lots of critters to blame that on - any of the scavengers (crabs, biters...) warpers (who knows where they might have put them) and even leviathans.