In Clive Barker's Jericho, the Jericho squad learns that there have been several predecessors (romans, templars and WW2 soldiers) before them. We later learn that the squad has to sacrifice itself in order to close the breach. It's not clear to me what this entails, specifically. If they would have to die, why would our squad encounter all the previous ones? What is the precise meaning of dying in the Box anyway? We learn that Ross didn't actually die when he was killed, but contrary to the previous Jericho squads he was non-corporeal.
Your link answers your question: They're not doomed to die. They have to sacrifice themselves, but not by dying.
When [the Jericho team] finally reach the point at which they can seal the breach, they decide that they should kill the Firstborn rather than try to reseal the breach, as resealing would just result in them being trapped in the Box and endlessly tortured until the breach was opened again.
Their sacrifice is not being able to return to real world (probably ever); getting tortured for eternity; and probably eventually corrupting similar to the Sumarian priests you have to fight as bosses during the game.