He'd probably like to return and have a shot at ruling if and when the current goons are gone. He's not interested in being in charge of a smoking ruin, which likely explains his reluctance.
Bingo.
He probably thinks it is 50/50 that it will collapse on its own.
He also thinks he could be the "unification" choice by having lived in the USA, being the Shah's kid (and descendant of Mohammed, the false prophet), yet against the attack.
Basically ride in on a white horse, saying "not my fault."