Jed Mercurio has said killing off the three stars of Line Of Duty is "never far from my thoughts".
The police corruption drama will return to television on Sunday with stars Adrian Dunbar, Vicky McClure and Martin Compston reprising their roles, and Kelly MacDonald joining the cast.
The new series will see anti-corruption unit AC-12 take on a new case regarding the senior investigating officer in an unsolved murder case.
Asked if he had ever considered killing off the "golden trio" of DS Steve Arnott, DI Kate Fleming and Superintendent Ted Hastings, Mercurio said: "Oh, it's never far from my thoughts, honestly.
"We all get on brilliantly, but everybody knows that we're serving something bigger than ourselves, which is Line Of Duty, and one of the things about the show is that nobody's safe; it's what keeps the audience on the edge of their seat.
"So, I know that it would be a sad day, but I think all the main cast realise that it's possible, and we talk about it, we joke about it, and it's something that no one would relish, but everybody would understand."
Filming of the sixth series of the hit show began last year, but had to be paused because of disruption caused by the coronavirus pandemic.
Mercurio said there was "no panic" when it became clear the production had to shut down, adding: "It was just looking at the science. We were in a situation where we had a little brush with coronavirus earlier, and we were able to do testing, so it was really straightforward.
"We tested the people who had possibly been exposed to the virus, they were isolated, we just worked through it and we carried on.
"But... we had another potential scare - in terms of people might have symptoms - and, at that point, for whatever reason the Government had withdrawn community testing.
"We weren't able to test our people, so therefore we didn't know where the virus was, and I just phoned Simon (executive producer Simon Heath) and it was a very straightforward conversation. I just said, 'I think we have to shut down', and he said, 'I agree, we've got to shut down'.
"So we filmed the rest of that day and, at the end of that day, I told the cast and crew that we were shutting down, and we then spent the summer waiting for a test and trace system to materialise and then came to the conclusion that we had to devise our own."
The show will return with seven episodes, rather than the expected six, and Mercurio said: "It would have ended early if we had done six, because we had more stuff.
"Actually, it wasn't the case of planning seven, it was just the effect of the interruption of shooting and when we went back, we ended up, for long periods, working with two units, for all kinds of reasons related to safety; getting through the shoot faster, being able to have crew who could step in if departments had to self-isolate.
"So that meant that we were able to shoot more additional material than we usually do.
"We tend to overshoot, because we tend to shoot a lot of explanations of things, and then in the edit we decide if we need them or not, whether things are clear enough without all the intervening stages being explained and laid out for the audience.
"And so, what we found was when got to the end, we had initially conceived having a 90-minute episode six, but with all the additions, it was pretty clear that it was going to be two hours, and then we got into a conversation with the BBC about the best way to handle that, and everybody agreed that it was to split the last episode into two, and that created episode seven."
Line Of Duty returns to BBC One on Sunday, March 21.