Ok, now, even if I think that I'm too low leveled to complain, I found in recent matches that even if a crewman left, it would be still be a manageable situation, someone else might join, or we'd would have to rely on the AI.
On the other hand, when the captain left, everything was almost totally screwed, in particular for the fact that only cap'ns have flight-helping tools, can command AIs
(we all know how AIs in "do as you were" mode are retarded), and activate respawns (before the the forced respawn anyway)
I think that after a crewman leaves there should be the possibility to change your class during the match, even more if the captain slot becomes empty mid-match.
Feel free to contradict me anytime