What happens if I don't "RETURN TO THE BATTLE!" in time?

When playing as Pathfinder in Apex Legends, I sometimes grapple to the top of tall terrain and suddenly see a flashing message appear in the center of my screen telling to me "RETURN TO THE BATTLE!", with a timer ominously counting down from 30 seconds.

It seems like the purpose is to keep players from camping in areas that are outside of the normal field of play and may be difficult or impossible for some legends to access. The scary message has worked on me: I've always made sure to get back in-bounds before the timer expires, so I've never seen what happens if I don't. But I'm often tempted to cut it close—these can be nice spots for sniping—and I'd like to know what risk I've been taking.

What happens if I fail to "RETURN TO THE BATTLE!" before the timer reaches zero? Am I disconnected from the server, like someone who goes AFK? Do I start taking damage as though I were in the circle? Am I teleported back to my teammates? What happens?

When the timer reaches zero you immediately die, without being downed first. You're not disconnected from the match, but your deathbox spawns where you died (like it normally does), so if you were on top of the map it may be practically impossible for your teammates to recover your banner and revive you.