1. Do we want to assume best play will happen and end games at 1/2 mafia, 1/2 VT?
I was kind of responding to this one without quoting it above. But basically, we don't need to assume "best play" necessarily...just that a faction won't knowingly kill itself when it doesn't have to. That way you can end with 1/2 mafia 1/2 non-killing single-voting roles.
So, you could say:
Mafia win-con: you win when it becomes impossible for a member of your faction to die without your consent.
If there was two mafia and a vig, mafia would win, but one of them would still die.
True. And if it were during the day mafia could just lynch the vig.
But, if it were a 1-shot bulletproof vig, mafia would not necessarily win. (assuming still bulletproof that night)
So, I think the win-con should always be stated as: Mafia wins when all town-members are mafia or nothing can prevent this.
So, what can prevent it?
1. If non-mafia has at least 1 more player than mafia, under normal rules, they can lynch mafia, and mafia can only kill one of them. After a sequence of 1-for-1 trades non-mafia has a player left, and mafia does not, mafia loses.
2. If non-mafia has equal players to mafia, and some means of killing a mafia player, then they can kill mafia and mafia can only kill one of them. After a sequence of 1-for-1 trades both factions are eliminated, and there is a draw. (or if town kill has priority (such as a double-vote would give, town wins)
3. If non-mafia has LESS players than mafia, and some means of killing one more mafia player than town player, then after a sequence of un-answered kills on mafia, we would be in one of the preceding 2 situations.
For 3, this includes any combination of: killing role + protective role or multiple killing roles.
In all cases non-mafia means anyone who is not part of the informed majority, regardless of win conditions.
So, in any of the above cases, assuming the win-con for mafia is "be all of town, or nothing can prevent", then those are the situations where "something can prevent" and the game should continue.
There are certainly cases where mafia has sufficient power that 2 or 3 are still mafia wins. At some point that crosses over into "assuming optimal play", which we should probably not assume?
example: goon+roleblocker v. VT+vig
mafia should shoot one, block the other. Either they block the vig and go 2mafia v. vig, or kill the vig and go 1mafia v. VT. I think it would be relatively safe to assume they do this, but you could make them submit the Night-action.
example2: 2goons+roleblocker v. 2VT+vig.
if mafia shoots or blocks vig, they win clearly. If they shoot and block the VT, AND vig shoots the roleblocker, you go to 2goons v. VT+vig. They blocked the VT, so they know the other is vig. They thus shoot the vig and go to goon v. VT, then win. I'm not sure how safe this is to assume. I think I'd play out the first night at least (they could obvi-win at that point anyways).