Sidenote - how likely is it for the remaining mafia member to be a non-robot role? Was it like, 46% or whatever the compliment was of the 'higher than 50%' possibility?
As i understand it, no more or less likely than anyone else being a robot
...well shit, then I guess a lot more roles became useless.

On another note, I'm -
pretty- sure that CleanOnion is not a mafia member, although if he is/was, being a policeman basically negates the possibility of his nightkill being blocked
ever, which would be one of the most powerful combinations in the game.

I doubt that he's a Criminal though - if anything, as long as we have Officers and one other nurse, this game should end soon anyway.
MID EDIT BECAUSE DEMAGOG POSTED BEFORE I COULD POST 
I think it's 17%? Pretty sure I posted somewhere with that number. It was 54% to start the game, but we know that only 1 mafia could be a robot (since 2 were impossible and 1 didn't roll robot). I think that brings the chance down to 33%. For some reason I halved that to 17%, but can't remember why.
Anyway, don't kill Onion yet. He is a kill we can leave for later, and the longer the mafia doesn't kill him, the more likely it is to be him (because what mafia would leave someone alive that can confirm civs). Most likely he will die next, so lynching him would be a waste.
Right now, 12 people are still alive. Assuming two people die every round starting now, we have five votes to kill the last mafia member. After the fifth vote it's GG. Calindu is confirmed civ, and it's still possible for scientists to figure out who the mafia member is.
Be patient and civs have this game in the bag.
Still don't know how those numbers are coming about Demagog. >_>
And I don't want to sound pessimistic or useless, but if the last mafia member
ISN'T a robot, then scientists are basically out of luck in doing anything investigative. I agree what you say about CleanOnion - but I'm more concerned about the possibility that the other policeman making arrests is either a) "afk", or b)
the actual remaining mafia, which we can't stop with any ability due to roleblocking prioritization/precedence over the other main abilities.