Only if the developer chooses to make their app price fall. They could keep it the same or raise it even higher than it was when it was in the App Store. It's their "art." They can charge whatever they want for it. The potential loser here is Apple in getting cut out of first in line for 30% right off the top.
If developer values the relationship with Apple enough to keep selling in the App Store, they keep allowing Apple to be first at taking that big cut. If developer doesn't value that relationship to trade 30% for it anymore, they can opt to pull the app and sell it direct so that THEY get to take that 30% for themselves... or some lessor amount if THEY opt to charge less for the app.
OR, dev could leave it in the store AND offer it direct. They'll make more money on the latter for customers willing to buy direct from them and less money on the former because Apple gets first cut of each sale. I've purchased many apps direct from app developers over the years for my Mac... some of which have also been for sale in the Apple Mac App Store. There was no real consequence for me either way but I like that the developer made more money for their app that I use. Apple is not exactly going to be destroyed by losing a little of that universal 30% cut of every app.
If I'm Apple or if I prioritize being a shareholder over being a consumer, I HATE this... because I know that all of the spin that's been spun for the last few years is about to be shown to be much ado about nothing. All of the EU will not be hacked. All EU iDevices will not be bricked. All EU iDevices will not be loaded with viruses. All EU bank accounts will not be emptied. Etc. Much like how the new iPhone would be a lint magnet, with a wobbly port and broken tongues galore turned out to be NOTHING, this too will turn out to be nothing like the fear hype that is slung around.
And once it is proven in a region as big as the EU to be better for consumers, there is rumor for the same consumer benefits to spread to other regions where other consumers may want the same benefits.
If in doubt, stand by and anyone can see for themselves. The EU will continue to exist and prosper, etc as any other region. They'll just have more ways to use their iDevices than the rest of us... and more options to buy select apps than the rest of us. And good for them!