I wouldn't really expect them to invade Iran quite frankly.
A couple of US aircraft are shot down and they tie the surviving aircrew to the next targets the US will go after, yep they would have to invade.
General Zinnin who is rational says it best.
(After youve dropped those bombs on those hardened facilities, what happens next? What happens if they decide, in their hardened shelters with their mobile missiles, to start launching those? What happens if they launch them into U.S. bases on the other side of the gulf? What happens if they launch into Israel, or somewhere else? Into a Saudi oil field? Into Ras Laffan, with all the natural gas? What happens if they now flush their fast patrol boats, their cruise missiles, the [unclear] full of mines, and they sink a tanker, an oil tanker? And of course the economy of the world goes absolutely nuts. What happens if they activate sleeper cells? The MOIS, the intelligence service what happens if another preemptive attack by the West, the U.S. and Israel, they fire up the streets and now we got problems. Just tell me how to deal with all that, okay?
Because, eventually, if you follow this all the way down, eventually Im putting boots on the ground somewhere. And like I tell my friends, if you like Iraq and Afghanistan, youll love Iran.))
And bombing a nuclear reactor which has a lot of Russians working at it, Vlad the Impaler would be slightly miffed over that.