Each withdrawing district shall remain liable for its share of the indebtedness of the capital costs of the cooperative school district which is outstanding when the withdrawal vote takes effect, and the withdrawing district shall pay to the cooperative school district annually (a) that percentage of the payments of principal and interest of such debt thereafter due which is the same as the percentage for which the withdrawing district was responsible in the school year immediately preceding the effective date of the withdrawal vote, and (b) all amounts of state aid for the purchase or construction of school buildings and any other state aids which are lost by the cooperative school district after the withdrawal of a district as a result of such withdrawal, as determined by the state board of education, except that the withdrawing district shall not be liable for any indebtedness or loss of state aid or other aid contracted after the district has duly notified the remaining districts in the cooperative that a withdrawal study is being requested. Payments in discharge of such liability shall be made in accordance with a schedule agreed upon by the school board of the cooperative school district and the withdrawing school district or, in the event they fail to agree, as fixed by the state board of education. Such payments shall be deemed to be trust funds and shall be applied by the cooperative school district solely in payment of its indebtedness which was incurred to finance cooperative school facilities and which was outstanding on the effective date of the withdrawal vote. A school district which withdraws from the cooperative school district shall forfeit its equity in any cooperative district schools.