Legal Question in Wills and Trusts in Missouri

I'm assuming that your mother's husband is still alive. Assuming the accounts were held jointly as husband and wife between them (technically, in Missouri, tenants by the entireties), the accounts are now the husband's alone. Your mother held two roles, one as a co-owner as to her "half", and the other only in a fiduciary capacity, that is, with apparent transactional authority. The Power of Attorney obviously has no validity anymore unless there was a successor named. Her authority died with her. If the Power of Attorney carried no successor then a conservator for the husband will be needed, but, given the assumptions above the fact that she operated on his behalf under the Power of Attorney are now irrelevant. It is the same result as if they were both competent and she died -- it's his.