EU politicians should grow some balls and force their companies to ignore US sanctions in cases like these
If you don’t follow sanctions, other banks either with branches doing business in the U.S., or their partner banks, will refuse to continue banking with you out of fear for not following sanctions – which include banks enabling sanction-circumvention. Essentially, even if the bank doesn’t want to deal with USD (which most banks would still like to do!), you’re still bound by the sanctions. A bank won’t survive long or well if it’s cut off from a majority of other banks.
China does this via laws that say, if you do not provide services to Chinese citizens/entities citing foreign sanctions, they can send you to a gulag forever. Seems to be fairly effective, considering how heavily sanctioned Huawei is.
All these hard "immediate consequences" scenarios are pure fiction. Not because they can't become truth, they can. But there's a hundred other possibilities. Literally sticking to the "letter of the law" is just one of them, and not a particularly likely one.