And thus lies Iran; the unelected Guardian Council vets candidates thereby stalling the system; 2,500 reformists in the 2004 parliamentary elections, 1,700 in 2008 parliamentary elections, 471 in the 2009 presidential elections. And even then, the unelected clown in chief will get his way against even the vetted successful candidates. This is partly why the 2009 elections legitimacy shouldn't be overstated: all of them lack openess and fairness.
(a) People decide whether they want an Islamic system or not once they have, then Islam decides everything else. There is no need for a referendum... Islam chooses the best leader for you. Not you. You can choose whether you want Islam or not.
(b) [If] the majority don’t want it, then religiously the govt. becomes illegitimate and it is an obligation for those in charge to step down