I agree with you Lorraine, Greg didn't die, the clue is in Gone to the Angels, don't go near anyone if you've survived a killer disease, so he would have wanted Jenny to think he was dead.
As I mentioned to Bob some years ago, I always felt that Blake's 7 could have been a follow up to Survivors Season 3. It was made the following year after all, however Terry Nation's widow has informed me this is untrue.
Season Three ended with an episode called Power with Greg becoming a political figure, whilst the hydro electric power stations were switched back on and there being fear about who sits in the control seat. Blake's 7 was about where the wrong people were in the control seat. The president of the federation was similar to Arthur Wormley, who wanted to "grab power" before anyone else did, Anne Tranter (who in the novel joined Wormley's mob) was similar in ways to Servalan in that she would join up with anyone who was likely to provide her with status, and Blake being similar to Greg in that he was the only person capable of rallying the people to overthrow tyranny. It would have been an interesting twist where instead of trying to get the technology working, they'd have had to destroy it, which would have taken the series back down the path of Terry Nation's novel, and indeed the follow up, Genesis of a Hero.