Shia Muslims have a strong martyrdom culture in comparison to Sunnis. This is why assassination of Khamenei didn't do anything in terms of disruption. He was martyred during the holy month of Ramadan and they welcomed it. All US did was created another honorable martyr for them.
I know it's difficult for Westerners to grasp how someone could pray for their own death but this is what they do. Decapitating their leadership doesn't do much because the next guy just takes over.
30% of the population in IRAN is composed of these fanatics and they will gladly give up their lives for IRGC. In a country of 90M, that amounts to a lot of people. IRAN has very difficult terrain and IRGC has been preparing for this war for the past 30 years. They don't care about the lives of Iranians, US can bomb Tehran to hell and they will not care. They have nothing to lose and will gladly sacrifice innocent people.
The Shia's motto is: "Every day is Ashura, every land is Karbala" [0], [1]
I think this is going to be a difficult conflict for everyone.
[0] https://en.wikipedia.org/wiki/Ashura [1] https://en.wikipedia.org/wiki/Karbala