There's no way to check how many players remain in an area with events. You'd need some win brick to trigger anything.
there is, it's just a bit difficult
to do this you're probably going to need zone events to detect when a player leaves the zone (dies), and check that there's only one player left in the field (spawn a zone, onenterzone increments a counter, check after a delay if the count is 1)
this will handle the death check, to teleport a player you will need to then spawn a zone on the lobby when the death happens, which teleports the first(?) person into the arena
as for teleporting the dead player, you might want to just have them spawn outside of the arena (teleporting something that doesn't exist is difficult)