Worst possible outcome right now: BSW gets just enough votes to make it into parliament.

This results in an unstable government, since CDU/CSU and the expected partner SPD don’t have enough seats, with no one willing to help form the government. New elections are called shortly after.

BSW can destroy parliament by simply existing (well, the voters who put us in this situation with so much AFD), and the only hope is that we throw out all their votes when they don’t reach 5%. I don’t think it’s likely, but it is possible.

EDIT: BSW didn’t make it, a boring stable, yet slightly right wing, government for us.