When the Cybermen flew into the atmosphere, they all burnt, and thus removed the clouds of "Cyber Pollen." However, we know that Lethbridge Stewart stayed behind for a short time, before flying away.
However, remember how one burning Cyberman started the clouds in the first place? Surely he'd have done the same if he'd burnt himself.
My theory is that he went off into space to explore, just like the Doctor. If you ask me, it's quite a fitting end that the character who spent so long defending the Earth from aliens is now out there exploring other worlds for himself.
That said, I wouldn't ever want to see the Cyber Brigadier again. It wouldn't be right. But I really like that Moffat tried to give the character some closure.
However, remember how one burning Cyberman started the clouds in the first place? Surely he'd have done the same if he'd burnt himself.
My theory is that he went off into space to explore, just like the Doctor. If you ask me, it's quite a fitting end that the character who spent so long defending the Earth from aliens is now out there exploring other worlds for himself.
That said, I wouldn't ever want to see the Cyber Brigadier again. It wouldn't be right. But I really like that Moffat tried to give the character some closure.
