Putin's condition for (a) would be (is) that Assad stays in power. I actually think the Americans (or more accurately the Obama admin) are coming around to this position, but it negates the need for (b) and (d). At this stage, an Assad victory or some kind of partition is looking most likely. As for (c), no sane government is going to want their troops involved in this mess, you really think the Brazilians, Indians, Nigerians, Irish, whoever are gonna like seeing their young guys coming home in coffins?
I also find it strange that your hopes for Syria are essentially dependent on the good will of a regime (Russia's) that you spend half your time vilifying on here.