While severance packages are not that common they do come up in divorce cases from time to time. Under Missouri law the answer to whether a spouse can get half of a severance package is based on what the severance package is meant to replace. Under a new 2014 case, Zahn v. Zahn, Missouri Court of Appeals, Eastern District-- ED99950 & ED99951, February 18, 2014 the issue is whether severance pay was intended to compensate the employee for efforts made during the marriage or to replace post-separation earnings. If the payment was intended to substitute for lost future earnings, or earnings that would occur post-dissolution, then the payment is nonmarital property of the earning spouse.
Of course these matters are always determined on a case by case basis. If you think you may be entitled to a severance package it is important to obtain a copy of the severance package agreement and review it carefully with an attorney. The company's intent with respect to providing you with the severance package is going to be a very important element with respect to whether your spouse is entitled to any part of it.