None of the guardians survived that raid, all were slaughtered by the darkness. All of the guardians ghost were obliterated, but one survived. The 7th ghost who followed the fireteam out of curiosity. This ghost had not yet found a guardian, and over a period of time in the realms of Crota, re-adjusted his view of light and dark and saw the traveller as the destroyer of worlds, and Crota as the protector. After accepting Crota's gift of dark matter; the ghost and Crota discussed how they could eliminate the traveller. And realised that they would first have to destroy the guardians. As such, Crota mixed the DNA from both himself and a fallen guardian, and the Ghost dutifully revived the guardian in a place where this guardian could escape; with selected memories implanted. Eris would send guardians on quests. The weak ones would be left alone (for the time being), whilst the strongest guardians would be sent to get rid of Crota - unaware, that they too would eventually cease to exist once Crota killed them. As for the weak guardians; when Crota rises, he will ask them to join him. If they refuse, they will be dispensed. Accept, and they will earn the gift of dark matter. [spoiler] And together, Crota and Eris will rule the galaxy as father and daughter... [/spoiler]