Chess board thinking only goes so far. There are far too many variables to say with any certainty that this and that will happen. Just look at the Iraq war. It was supposed to take a few weeks, then ended up being a 9 year fiasco.
Keep in mind that Iran is a bigger country than Iraq. Very mountainous, meaning slow advance and lots of combat. It is a far wealthier country than Iraq, meaning better weapons. The population of Iran is young, something like 45% of its people are under 30 years old, meaning LOTS of able body young fighters. Iranians are very patriotic and have grown up with the Islamic Revolution and have little exposure to western culture, meaning they are not all secretly wishing for McDonald's, Super Bowl commercials, and "American freedom".
A war with Iran will take a long time, and will be very expensive in both money and lives. They are not fools, and have been preparing for an attack for many years. Casualties will no doubt be more like Vietnam, as opposed to Iraq. If the Iraq war cost several trillion dollars, how much do you think an attack on Iran will cost? And is it really worth it?