If the father does not transfer the business into community property, and if he dies without a will, the son would be entitled to half the property if there are no other children. If there are, he would have to split the half share with them. If there is a valid will, the property will pass according to the will.
Your son would qualify to be an heir, whether or not your husband had a will.
However, your husband may have made separate arrangements for the business to be handled where it may not even be included as part of his estate--it could easily go out of business or acquire a lot of debts to where the business might not be as valuable at the time of his death as it is now. Hopefully, that won't happen and the business will continue to be successful.
What you really need to do to protect your son's interests is talk to your ex-husband about what estate planning has he done. Has he prepared a will yet--if not, then he needs to do so as soon as possible. Ask him what does he intend to leave for your son? Are there any life insurance policies that name your son as beneficiary? Ask him who will be the executor of his estate and could he please furnish you with a copy of the will or at least let you know where the will is kept.
It's better to find out ahead of time instead of after he dies, when it is often a confusing time and people are reluctant to give out information because they are grieving.