While the idea is nice, it would be impractical form a co-op campaign point of view. Even if there were survivors still on board that ship, other than MC, they wouldn’t be spartans. They’d likely be marines. Doubtful we’d play as them.
I’d rather the first mission begin when the ship crash lands into the shield world and MC meets up with the survivors from Ghost of Onyx. That would make for a viable co-op campaign. I mentioned this in another thread. Halsey would likely be with them, so the first mission could be to secure a place for Halsey to set up base camp while the players explore the shield world to find a way back to UNSC controlled space.