I collaborated with my daughter on a fan-fiction writing exercise that included Destiny and I came up with an idea that's relevant to this discussion. I posited that ghost resurrection is what keeps guardians as seemingly "immortal" as they are. They don't seem to need to eat or sleep or even rest, can't really recall their past, because they are constantly "new" entities, built from the entropy of their old, deceased form. In my tale, a guardian walked away from the fight to live peacefully and alone, and as the months and years went by he slowly started to need to eat and shit and sleep, developed other emotions and relationships, started to remember his past. In this situation he began to fear death as much as any "normal" person because he feared he'd lose the "humanity" he had regained. He also began to suspect his ghost of trying to get him killed, to get him "back on the program", and that was a whole other narrative twist. I like the idea, but it seems to fly in the face of what Bungie presents here, as Saladin has evidently not seen a lot of action over the course of centuries and he still hasn't aged and seems as focused and detached as other guardians are. I do agree that guardians seem to not just be immortal, but bereft of physical needs outside of absorbing Light. It's a wonder they aren't all mad and suffering PTSD, considering they are little more than walking talking instruments of war with no agency or private lives of their own, seemingly anyway.