Back in the day I was a kid and had a subscription to Dynamite Magazine, remember that? And they had a write up on the second season of Space: 1999 and they said Victor was supposed to be written out of the show by way of a heart attack to make room for the new shape shifting character of Maya.
I haven't seen it since it first aired and haven't rented any of the DVD's so I have no idea of they even filmed but but I remember expecting to see Victor die in the first episode of the second season. Maybe someone who has seen the DVD's know if it is mentioned in the commentary or in a special feature or something.
Oh look! I found the cover!
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.