Twitter is just burning money every minute as it is. Even if the EU only fines them a symbolic 1 Euro, it’s going to keep losing money. The important thing is that the fines / punishments will probably get bigger if Twitter continues to break the rules, so it’s likely going to stop.
How’s it going to stop? A responsible, intelligent company would hire moderators and chase off the Nazis. But, Musk will most likely just make Twitter unavailable in Europe. That will just accelerate the doom spiral.