He wasn't seen on the roof -- that's my point. I rewatched that episode last night; the camera panned the roof, and Chuck wasn't on it.
The writers left the impression that he'd been on the chopper, which crashed and Susan had all the sad, then *POOF* hero Chuck arrived on the elevator, bagging an unknown patient who also wasn't on the roof. His spleen rupture, saved by St. Abby, happened after he'd been downstairs for awhile.
I always saw Susan with a nice doctor, maybe one who worked in an office rather than with long ER shifts, to create relationship tension. Not with Chuck the