Hangars are individual components so they will not chainreact. Fighters I believe are just ejected, but they might be destroyed. I've only lost hangars with fighters on-mission so the hangars were empty (except for some unlucky redshirts). And good luck with that missile swarm.
Will hangar bays cascade if one is hit and destroyed? What happens if a fighter is in the bay? Never have I lost a carrier before, now it looks that all 6 in the Terran fleet will be destroyed by a huge missile swarm.