If Iran have assets worldwide, US and EU would already freeze them as they did to Gadafi, but they can't, because they are in Iran. Iran evacuate assets home same as Venezuela did.Iran has assets worldwide that could be seized and serve to repare the prejudice.
If Iran breaks the contracts, the price it will pay such thing could be very heavy.
Also, freezing of banking assets is one thing. Seizure of the assets is quite another.
Iam expecting Monday to be a tough day for all the European countries...
If there is an existing contract to supply a commodity that is done on either state level or company to company level. There are always provisions and clauses in such a contract and penalties of course.
I can not imagine that all long term contracts with EU countries would all suddenly end in July. There might be some contract breaking on the EU side.