Quote Originally Posted by RyougaZell
I really wonder how you came to the conclusion that Sergei is alive. I really do.
Sunrise can't be trusted to actually kill characters it portrays as being killed except (maybe) by declaring the franchise itself dead. Thus there's no reliable evidence to dispute the possibility that Sergei will come back, having been conveniently rescued by and then defecting with Kati and Patrick after the elevator incident.