Notwithstanding the commencement of a legal action for determination of domicile within this state or the commencement of an arbitration proceeding, as provided in section 4, the commissioner of revenue of this state may in any case enter into a written agreement with the other taxing officials involved and with the executors to accept a certain sum in full payment of any death tax, together with interest and penalties, that may be due this state, provided this agreement fixes the amount to be paid the other states involved in the dispute, at any time before such proceeding is concluded. Upon the filing of this agreement with the authority which would have jurisdiction to assess the death tax of this state, if the decedent died domiciled in this state, an assessment shall be made as provided in such agreement, and this assessment finally and conclusively fixes the amount of death tax due this state. If the aggregate amount payable under such agreement or under an agreement made in accordance with the provisions of section 3 to the states involved is less than the minimum credit allowable to the estate against the United States estate tax imposed with respect thereto, the executor forthwith shall also pay to the commissioner of taxation of this state the same percentage of the difference between such aggregate amount of such credit as the amount payable to such commissioner under such agreement bears to such aggregate amount.