Mo. Rev. Stat. § 456.1060: Disposition of unappointed property under released or unexercised general power.

To the extent a powerholder releases or fails to exercise a general power of appointment other than a power to withdraw property from, revoke, or amend a trust, and except as provided in subsection 3 of section 456.995:

(1) The gift-in-default clause controls the disposition of the unappointed property; or

(2) If there is no gift-in-default clause or to the extent the clause is ineffective:

(a) Except as otherwise provided in paragraph (b) of this subdivision, the unappointed property passes to:

a. The powerholder if the powerholder is a permissible appointee and living; or

b. If the powerholder is an impermissible appointee or deceased, the powerholder's estate if the estate is a permissible appointee; or

(b) To the extent the powerholder released the power, or if there is no taker under paragraph (a) of this subdivision, the unappointed property passes under a reversionary interest to the donor or the donor's transferee or successor in interest.