The Bundesrat is composed of representatives of the state governments. That is, if there is a coalition government in a state, the state's representatives will have to represent all coalition parties, which means abstaining in case of conflict.

It's not CDU but CDU/CSU+FDP that is losing a majority: with the representatives of states with CDU+SPD, CDU+Greens and CDU+FDP+Greens governments, the CDU/CSU will continue to influence the vote of a big majority in the Bundesrat, regardless of what coalition forms in NRW now.

_{*Lunatic*, n.
One whose delusions are out of fashion.}