Ultimately we don’t know what happened to Ryley after he left in the Rocket and headed on his way back to earth. Since a message says he isn’t allowed to land until he pays off a trillion credits it’s possible he decided he needed to make a deal with Alterra and be saved in their NoA reprinting system as a “long term” employee until his debt is paid. Would be interesting to find out what happened to him in Subnautica 2, and see if his story is somehow related to the events taking place there. Could be something deep into the story like he’s already been to this planet before the Cicada ever arrived, or something as simple as one of the characters that can be selected at the beginning of the game is a guy named Robby with a mysterious history.