Sorbate doesn't kill yeast. It only prevents them from being able to reproduce. So, you can still carbonate naturally with sorbate. The results are just harder to predict than normal because of the lack of reproduction. If your fermentation time is short, they'll still be eager to carbonate, although it does take longer than for beer, maybe 4-6 weeks on average instead of just a couple weeks. Another cautionary thing is that they might even cause gushers, and that's happened to me more than once. But if fermentation time is long and drawn out for months like I do, then the yeast gets tired and weak and can't reproduce, so natural carbonation from priming sugar happens about 50/50 in my experience, just as often turning out flat as carbonated, and never gushers.