Nothing. I'm glad I have a couple decent guns already, although I don't have an AR. I'm not going to buy at inflated prices, so I'll wait. It's amazing how slim the pickings are around here. One place I know had a case full of Wilson Combat 1911s. Now they are sold out of those. Go figure!
If ARs do get banned, there is no realistic scenario I can think of where a more conventional gun will not work nearly as well for home defense. YMMV