Seeing how devs generally treat the topic of health and illnesses, I think they'd use the same tactics with disabilities. Euphemisms. None of the illnesses in the game, including the ones in doctor (and veterinary) have real-life names and symptoms, all are treatable, none are deadly (except the death by hamster I believe). So it might be things like prosthetics options in CAS, therapist career to help Sims with mental states etc - things to represent the idea of disabilities without including all of them or any in particular.