I'm something of a Space:1999 geek.
Barry wanted off the show after Season One due to creative differences with Gerry and Sylvia Anderson (the creators and producers.) Add to that the hiring of Fred Freiberger (season 3 Star Trek producer), widely regarded as a hack of a producer.
When Season 2 of Space:1999 premiered, no mention was ever made of Victor Bergman (or Paul Morrow and David Kano, either.) New characters Tony Verdeschi and Maya were introduced.
But, in the novelizations of the show, it was mentioned that Victor had died after his spacesuit failed while he was on a mission. Supposedly a scene of this discussion between Commander Koenig and Dr. Russell was filmed, but cut.
Thanks for the info. Now that you mention it, it does seem vaguely familiar. I read some of the novels so maybe I read the one it was in.
IMO, the one with the spider monster in the graveyard of ships: Scariest. Episode. Ever!