Orwell wrote:
Popular protests can stop military coups- there was an attempted military coup in 1991 in the Soviet Union, complete with jamming communications and media, but protesters stood outside the Parliament building and defended their elected representatives against usurpers. After a brief standoff, most of the military defected, unwilling to fire on their own people, and the coup was defeated.
A similar situation is possible in Iran. Just a reminder that the victor is not always the one with the most guns. Still, I think the situation in Iran is more likely to play out like the situation in Zimbabwe- perhaps Mousavi will be given some government post as a consolation prize, but Ahmadinejad will retain real power.
That may be the case if the Basji militia men had a particular affinity to the largely urban dwellers who support Mousavi or if there was fractionating in the armed forces. But I don't quite see this as the case. Time will test my assumptions.