There is no doubt that sh**stain deserved to get blowed the F up. His actions did cause american deaths, and he was reviled by other countries as well as his own people. Currently, 1500 Iranians are dying per week as a result of his crackdowns, etc - per multiple Iranian twitter accounts at least.
However - and there is a pretty big however - facts are facts.
The US assassinated a foreign military leader in a 3rd party country.
He was in the car with the Iraqi architect of the embassy attacks - likely because he's the one who instructed him to do so.
Iran's power lies in it's capability to deny/interdict oil transport.
Iran, in order to save face, MUST act out revenge, with the likely targets being American bases and lives - and depending on circumstances - oil production and refining.
Iran has a lot of options, unfortunately - their active service military is around 600,000, with an additional 300k in active reserves, and up to 11 million able to be called on for the volunteer force.
Limited/No escalation - may be enough to save face while not actively escalating.
1. Limited cruise missile strikes against American/Oil targets
2. Strait of Hormuz increased patrols/saber rattling/seizure of oil
3. Strait of Hormuz sea mines/mini subs/attacks on Oil vessels
4. "Activation" of pre-established Quds terror cells in Arab world, "death to america" type stuff, embassy attacks by the local populace
5. Area denial to entire Persian Gulf
Escalation
1. Full scale missile attacks on surrounding countries Oil production
2. Full scale missile attack on american bases anywhere from Afghanistan to Israel
3. Land based missile attacks on US Navy bases/vessels
4. Mobilization of massed forces on Iraqi or Syrian separatist borders and/or invasion as "liberators".
Of the above, I think 4. and 4. are most likely, at least initially.
If it goes to full scale war, the US wins, period. Russia won't defend Iran with it's own forces, it can't afford to. The other Arab states might, but most likely would be limited to insurgent actions.
BUT - I don't think Trump thought enough about this. I think this was a kneejerk reaction to the embassy, i.e. "what can we do to hurt them bigly" and some hawk obliged. It's becoming a scenario that is becoming impossible to back down.
If this goes to full-scale war, the order of battle is stealth attacks on command and control and air defense sites, followed by land-land missile sites, followed by power generation, followed by SF insertions to take out any underground biological/nuclear capability. Somewhere along the way, the land-sea missile sites would be taken out. As always, once air superiority is gained, the US would own the skies.
Invasion is not a possibility, we won't be able to topple the government and install another one (again), and likely Iran remains a pissed off radical islam country.
But there will be loses, and those losses are going to be magnified due to presence of S-300 launchers and relatively advanced weaponry (compared to Gulf War I and II).