I thought the brother looked down and saw him swimming away. It was very far away, but there was definitely something moving in the water. I assumed it was the policeman. But even if he did survive, did his phone?
OTOH, seeing that the games are still running a year later, it would appear that either he died, and/or his evidence was never transmitted, or destroyed. But maybe it just got swept under the rug by someone powerful in connection with the games.
If there’s a second season, I’m certain either he survived and is waiting to try and infiltrate again, or he died but someone received or intercepted his evidence and will follow up. I feel like this is the kind of show where the former is more likely.