Plenty of what you said is plausible. I don't think ISIS is ever "finished". USA always maintains it as a strategic asset.
USA has learned a heck of a lot in recent times.
Why send in American troops when some dumb zealots can do the job for you? ISIS were only barely thwarted in Syria thanks to massive Russian assistance and massive collateral damage, which actually did a lot of harm to Iran's image in ME. Syria was a costly, pyrrhic "victory" for Iran, while USA didn't even commit massive ground forces at all. USA certainly failed its overall objective but it still beat a reasonably ordered retreat.
Look I'm no expert or even a quarter of one. I just think Iran will not be able to inflict significant human casualties on the Americans, which if you understand your history, (I.e. Vietnam) is the ONLY rate-limiting step to American ambitions. Sure, I lack knowledge on Iran.....but I know the American mindset. No peace movement, million man march, international law, UN pleas, Russian verbal threats, Iranian civilian deaths, refugees crisis ain't gonna do squat to convince USA to stop.....ONLY US SERVICE PERSONNEL IN BODY BAGS suddenly gets them singing kumbayah and holding hands for peace.
I actually hope you're right and Iran foils the American schemes. Honestly I do - for selfish reasons mind you.
ISIS only managed to be successful in the beginning of their campaign because they faced no worthy resistance. The Syrian army were worthless and busy fighting the rebels. I believe they are still worthless. The Iraqi army lacked spirit and didn't put up a fight against ISIS. They fled the battlefield. There really was no one doing resistance. Syrians still prove to be worthless, Hezbollah from Lebanon, Afghan, Iranian and even Pakistani volunteers had to save the Syrian Army. Putin didn't start bombing ISIS before ISIS was almost finished off.
In Iraq however, under right rule and motivation, the Iraqis proved to be very capable fighters. ISIS stands absolutely 0 chance against the Iraqis now, they would demolish ISIS.
You are right about one thing though. US wont stop at anything unless they start seeing dead bodybags with American flags on them. The difference between Iranians and Americans though is that when we see a dead Iranian, we get angry and want revenge. When Americans see dead Americans, they get scared and piss their pants.