I don't know if the Scions CAN die. In theory they're the same type of being as we are, and our ability to resurrect at aetherytes is an explicit power afforded to us by Hydaelyn, not a case of gameplay and story segregation.
I even seem to remember a conversation to the effect of that going on between the scions, but they don't KNOW they all have the same power and thus aren't really keen on trying it out just on the off chance it's exclusive to us. Pluuuuus remember what Leviathan was able to do with that one priest.
Being one of Hydaelyn's tempered is a real crapshoot.