General info post regarding mortality.

If your character's body on Earth expires while they're Zoning in REM, both die. If their Zone-self expires in REM, only their Zone-self dies, and their Earth body loses its link to the Zone entirely. So that's it. Game over.

If a character's Zone-self expires while using the Nexus Projector, however, a fail-safe expulsion system will eject them from the Zone and back into our reality, effectively translating to "unlimited lives" as long as they use the Nexus Projector.