It's not that they wouldn't care he supposes - but right now Rey's importance is tied up in the mission. After will come more of the guilt from all parties, but Cassian can't imagine them taking her, not unless he and Jyn didn't want her. And that's not an option.

When Rey grabs at Jyn's finger and tries to inhale it, some of that hollowness in his chest dissipates and he smiles again, faintly. He can't just waste away anymore, not with Rey filling up so much of him. If there was anything good in him, Rey got it all, but he's okay with it.

Cassian brushes at some of her hair, feeling warm, and it's welcome against how awful the air was. "I like the sound of that."

Does he mean the 'ours' or the 'Rey Andor,' honestly he probably doesn't even know. Maybe both. He turns on the soft voice again, talking at her. "I bet she does too."