As much as the idea of resorting the monarchy of Iran appeals (as it also does for a number of other countries) to the sensibilities of many on this forum, doing so is a legal and constitutional nightmare - what for example, do you do with property that may have been sized by the state? Former presidents? Was the republican regime that has hypothetically been abolished an illegal one and if so should there be punishment for those involved?
Iran has a lot of problems but it's current political system has the means and opportunity to grow into a stongly rooted constitutional democracy as it's got something that the old Pahlavi monarchy lacks - a myth of blood sacrifice and popular mandate. Too many of the present Islamic republics critics and detractors get hung up on the Islamic part and overlook the republican elements of Iran. These republican aspects along with the fact that Iran has a long history of constitutional government, however flawed, is a strong history to build on and should not be underestimated - it's hard to see how a dyansty whose main contribution to Iranian policital culture was a fairly crude authoritarianism, however well meaning, could be merged with this. (Before you reply I am aware of the economic and social reforms that were undertaken during the white revolution)
Traditionally the Iranian monarchy drew its legitimacy from irans pagan or zororastrian traditions and later from the Shahs standing as the champion and protector of Shia islam, along with the idea of Iran as a great power. The Pahlavi's abandoned this defence for their regime and in effect relied on foreign backing and to a greater or lesser extent force and coercion (although recent research shows that there were greater levels of popular support than previously conceded). This sense of having abandoned their traditional religious role along with the perception that they were foreign puppets was a major factor in undermining the Shahs legimatcy in the eyes of a lot of people in Iran, along with other factors such as the fact that the Pahlavi's were a dyansty of recent vintage - a number of upper class Iranians saw them as illegetamte and still saw the Qajar's as the legit dyansty of Iran, including Mohammed Mossadegh who was a distant relation of theirs (it was a major source of friction between him and the shah and the main reason Mohammed Reza was willing to go along with operation Ajax in 1953). As one of MR's biographers Abbas Milani has pointed out he had no doctrine of kingship to fall back on to defend the regimes existence, along with his perceived end lack of national zeal, it's not too hard to see why those disolutioned with the shah might turn to political Islam. There is of course no reason why irans exiled dynasties, both the Pahlavi's and the Qajar's could not return to Iran one day as honoured citizens but has heads of state? I don't think so.