IMHO the real danger right now are parts of the conservative party that might do an internal take-over to reverse the decision not to do a coalition with the AfD (similar to what happened in Austria a few years ago). The current, rather broad spectrum protests might hold them back from doing so, at least right before an election.
The AfD is unlikely to ever get a majority by itself, so what really needs to be prevented is the normalization of their discourse to the point that conservative parties feel emboldened to help them raise to power, just like what happened with the historical NSDAP.