I think AfD's rightward turn would have happened anyway, but if AfD had gotten in in 2013, there would have been more moderates in an "entrenched" position (most importantly in the Bundestag, of course) and it would have been more complicated to oust them.
In 2013. AfD missed the 5% threshold by just 0,3% of the votes. What do you think would have happened if the party had passed the threshold and had a majority together with CDU/CSU? I guess back then the AfD was a more moderate party than it is now, so it wouldn't have been excluded from negotiations?
They wouldn't have been excluded from negotiations, but it's not clear that they would have wanted to be part of a coalition that early in the party's life.
I'm not sure. Right now it's easy to recognize Lucke and co as the moderates they were, but the overblown vitriol against AfD as supposed "Nazis" was very much real at the time as well. People were whipped into a frenzy over the breakthrough of a party to the right of the Union. I don't think they would have been invited to coalition tals (and yes, whether AfD would have wanted to take part in such talks is unsure too).
