Does my dad have a case?

My father was a Dentist for a Hospital. He was diagnosed with type 2 Diabetes several years ago. He currently has to take insulin shots and if his sugar drops significantly he needs to consume glucose tablets. He previous employer was aware of this condition. My father also indicated to the staff what they should in the case he passes out or has other symptoms associated with low or high blood sugar. He showed his assistants where he keeps his insulin and glucose tablets. Prior to his termination without cause, he experienced a symptom of low blood sugar. He had a patient in the chair and was waiting for a filling to set (this usually takes 10-15minutues) he closed his eyes and his assistant tapped him on the arm to alert him and continued on. Someone in the office later that day sent an email to corporate saying he was falling asleep on the job. The next day he was called into a meeting and terminated without cause. He was given 3 months of pay. This was a single event and had never happened before. Some other things you should know: There were originally 2 dentists working, my father and a co-worker. The co-worker was terminated for drug abuse; he was addicted to pain killers. He had complaints listed on his dental license, which they did not catch until it was too late. Needless to say my father was working double duty for the last several months. He was one of the top 5 grossing dentist in the company. Would this make a case for a violation against the ADA?type 2 diabetes