(a) A new trustee, or new trustees, may be substituted for the original trustee, or trustees, of trusteed assets in the event of a vacancy or for other proper cause. Any such substitution shall be subject to the commissioner’s approval.
(b) If the trustees of any trusteed assets heretofore created are individuals, and if the number of such trustees is reduced to less than three by death, resignation, or otherwise, the commissioner shall require that there be substituted for such trustees a bank or trust company in this state approved by him.