The EU will fall in line once Iran leaves the deal as well, and not a second before - that much is clear already. They have committed themselves to their strategy.
Large internationals will stop dealing with Iran, some small businesses with no US market will continue. And the set of companies is not static. We all have to earn a living. If you don't want to import Iranian pistachios anymore, someone else will.
Which is why the sanctioneers are so obsessed with shutting down SWIFT, and angry at the proposed vehicle. Because unless it's prohibitively costly to exchange money with Iran, someone will do it.
Iran is going to sit still for a while. They will navigate the waters as best they can, which may include showing some restraint at times, but things have to get much much worse economically before you see the total withdrawal you are predicting.
Assuming their internal situation stabilizes, which is not an unreasonable assumption at this point, Iran will at some point in the future declare that they do not consider themselves bound to the deal anymore, while emphasizing again that they do not seek a nuke and never have, and without initially escalating. They will then rebuild their nuclear infrastructure in steps and initially in secret whenever, trying to limit then fallout, as they have done before.