No, what will happen is what ALWAYS happens I a country under attack:

People will rally behind the flag to repel the attacker/invader.

And as shown by Iraq and Afghanistan, just because you militarily defeat a nations army and occupy, doesn't mean you won't have to deal with YEARS of guerilla fighting.

Iran falling would break containment and could lead to an even worse version of Libya, one that destabilises the entire region, the entire OIL RICH region...