AFAIK the risk of mandibular nerve damage is not that high since Zarrinbal requires a CBCT scan to be made beforehand, so he can easily identify the nerve's position. Still, could happen that the nerve is disturbed somehow. There's no guarantee of success. I had zero nerve damage myself, even when the chin wing was combined with a BSSO.
A higher risk is that of significant introduced asymmetry, which happened to me and some other chin wing patients. A crooked chin does not look good, trust me. I had to get a revision genioplasty for that. Also, Zarrinbal really likes to exaggerate movements to create dramatic effects it seems. He's not always very subtle. Not everyone looks good with a heavy jawline or a massive chin. A couple of post-ops he flipped through during consultation looked pretty horrifying (jawlines/chins like The Joker), for instance. Ofcourse, maybe that is exactly what those patients wanted, and he simply obliged them. In that case he cannot be blamed I guess.