Cayde wouldn't have needed to bring out his Ghost to heal him if he hadn't taken so much damage in the first place, but he needed his super. The whole time the Scorn pummeled him on the ground, Cayde was going into his menu to switch his super. Destiny 2's terrible load times killed Cayde! Edit: Apparently this is a spoiler to some people, and for that I apologize. I just thought everyone knew because said spoiler is pretty much everywhere by this point.