The issue with the CDU/CSU is that they already made steps towards the AFD after the party passed 20%. Remember, the conservatives in the Weimar Republic supported the Nazis, not because they liked them, but because they thought they could puppeteer them, get rid of the communists and socialists and then zhrowing them away and come out on top.
I am afraid that the current conservatives have similair thoughts when it comes to the AFD.