The governing body may sell, or give to the state of New Jersey, for military or armory purposes, or both, any real estate heretofore or hereafter acquired by the municipality for park purposes, and in the judgment of the governing body not needed therefor, and may cause to be executed good and sufficient conveyance or conveyances therefor. The municipality may impose as a condition of such sale or gift and conveyance a covenant that if the state shall cease to use the real estate for military or armory purposes for two consecutive years, it shall forthwith revert to and become vested in the municipality upon payment by the municipality to the state of the value of the improvements thereon at the time of reversion, but such reversion for nonuse shall not occur, if the nonuse is occasioned by, or occurs during the time the United States or this state is engaged in war, or the suppression of rebellion or armed insurrection. Should the municipality and the state be unable to agree upon the value of the improvements, it shall be determined by two appraisers, one to be appointed by the governor and one by the municipality, and if they are unable to agree, they shall select a third and the decision of said appraisers shall be final.