My son had bi lateral pars, Broke both l5 vertebrae (ears or spondy as they called it) though not at the same time. We did take a couple of weeks off seeking several opinions from different specialists. Never needed a back brace and started rehab work about 3 weeks after diagnosis. Looking in the mirror he was physically strong however his core was weak, that where the rehab was extremely beneficial. Son missed his high school season but is playing summer ball currently with no issues. There are specific warm up exercises and continued training that he does to help protect that area and so far so good. Spondylosis is not a baseball death sentence for everyone. Hope your son can continue his career.