It doesn't matter - when a strong and stable political structures suddenly collapse, the state fails and disintegrates due to the political infighting. While I agree with you that the chances of Iran becoming a completely failed state is unlikely, I do see an imminent civil war in Iran's future if a regime collapse happens, and the Americans and Israelis install their Shahi (royal) puppet there. A regime collapse will of course mean Iran will lose its sovereignty (probably for a decade or more), till a truly independent stable polity emerges form the ashes.