Considering how far backwards companies bend over to make business in China and some Arabic countries I don't expect a single company with some profitable business in the EU to leave that market.
So what? Nobody is obliged to serve any market, or a markets obliges to open for individual companies. If company A won't, companies B and C propably will.
If by market leader you mean creating monopolies, or oligopolies, there are rules againstt that in place. So there seems to be some concensus of seeing those outcomes as non desireable. And those rules cover consumer protection and choice, Microsoft has some experience with that when it comes to Internet Explorer.