A felony is not a per se ground of deportation. The immigration judge must determine whether or not the statute of conviction triggers deportability. Crimes of moral turpitude, controlled substance violations and domestic violence cases can trigger deportation. Depending on the length of residency, his immigration history and personal background, even if he's found to be subject to deportation, your son may have relief available.
You should consult with an immigration attorney who is skilled in deportation and family based immigration prior to proceeding on any course of action. Attorneys who practice immigration law are practicing federal law and therefore you can hire an attorney from anywhere in the country (as long as he/she is licensed).