I haven't put much thought on that, but seeing this, the germans are screwed, probably this will develop in a western slav-dominated Germany, with Saxony and Bavaria as germanic remains. But one thing, this will certainly cause a divide between High and Low German cultures, so...even less reasons to have a Germany.
And with the little research in wikipedia that i made now, i can say that we're not even far from the beggining of slav statehood, the Obotrites formed a confederacy in Pomerania that managed to conquer Schleswig by the end of the 8th century and Great Moravia was established in the beginning of the 9th century.
Heh, probably i'll need to make an update on Germany