Sometimes when you have had a gap or lapse in auto insurance coverage it can be difficult to get decent rates when you decide to obtain insurance again. Having prior insurance can give you a discount on a new policy.
So your son would likely lose some discounts, such as renewal discounts and without having an insurance provider for a year or so. Also some insurance companies may not choose to insure him. Some automobile insurance companies will not write you a policy without at least six months prior insurance.
If your son has a clean driving record it should help his insurance rates. Also to make up for the extra insurance expense your son may receive due to not having previous coverage in the last 6 months he may want to see if other discounts are available to him.
Other discounts that may be available could include: safe driver, a discount for the safety features on your vehicle, etc. If your son decides to go without auto insurance for a year or so he can come to us when he is ready to get a new car and obtain an affordable auto insurance quote with companies that will insure you even after a gap in insurance coverage.
Your son may want to think about getting a non-owners policy during the time in which he does not own a car instead of getting rid of auto insurance completely. This way he will have continual auto insurance on himself. A non owners policy would give your son insurance coverage while driving a friend's borrowed car. The non owners policy would work as secondary or excess liability coverage if he was in an accident and the damages extended over the car owner's limits.