Yes, it is possible to retrieve sperm by aspiration of the epididymis or testicle after vasectomy. However, it may happen that no sperm are obtained.
Therefore, it is usually recommended to freeze a semen sample before undergoing this method of male sterilization. The frozen semen sample can then be used in the future if gestation is desired through artificial insemination (AI) or in vitro fertilization (IVF).