The only other possible acceptable outcome is a borderless Europe.
It may take awhile but I think that is the future of Europe. Inside the EU people can live where they want, work where they want, no borders.
So it will come to another "Völkerwanderung" a wandering of people in the next hundreds of years.
The counting of minorites, the majorities oppressing minorities or ethnic cleansing will be problems from yesterday...
Will ethnic groups clash with each other? What if the law Poland has against Germans to buy lands ends in few years? Poland a full member in the EU, Germans able to buy land in the old territories again? Will be interesting to watch....

(That is the same with nearly every region Germans once settled in)