NASA would of course never turn off ***their ***communications, I assumed that was a given. I’m saying that as the two men in the LM started to asphyxiate they may have chosen to turn off their mics. Lovell famously disabled his medical monitor out of frustration during Apollo 13 (I don’t know if the other two actually followed suit as in the movie) but I seriously doubt Armstrong or Aldrin would have disconnected theirs in that situation, specifically not.
And they may have left the mic on. They were steely-eyed test pilots and were certainly very adherent to situational awareness. And leaving their mics on wasn’t going to hurt them at that point. But on the other hand, they were steely-eyed test pilots*!* They weren’t the kind of guys that would want their emotional death throws broadcast to the world, knowing that it wasn’t going to help them at that point either. Remember Aldrin turned the mic off while he took communion after landing (he had cleared it ahead of time)…