Without having all the information I need to be able to evaluate your son, I can’t tell you completely about his specific risks. With aortic valve insufficiency of grade 2, which would be approximately mild, his risks would likely be low. But, the anatomy of the valve is important here, as I don’t know if this is a bicuspid or tricuspid aortic valve (the latter being normal). A bicuspid aortic valve is more likely to have progression of aortic valve insufficiency as well as dilation of the aorta over time.
If there is no aortic valve dilation, the regurgitation remains mild, and the left ventricle remains normal size, his risk should remain low over time. There is no medical literature to imply that a patient with JUST these findings have sudden cardiac death. This means, as you have already implied, that he will have routine follow-up. If he is considering this as a career (and is good enough to play professional basketball), there is a high likelihood that a contract would include a clause mandating routine follow-up with a cardiologist. That said, basketball does include a fair bit of both aerobic as well as some isometric activity (especially as players progress into college and professional play). We believe that there is some increased risk of progressive aortic valve disease associated with isometric activity, although it is difficult to predict to whom and when it will happen. Typically, aortic valve disease is present in one way or another throughout life and does not go away. It may be that if there is progression of his valve disease, you and/or he will need to make a reassessment of his career plans.