In the event all the tribal assets, susceptible to equitable and practicable distribution, distributed to the mixed-blood group under the provisions of section
677i of this title, are not, within seven years from August 27, 1954, distributed to the individual mixed-blood members as contemplated in the plan to be adopted in accordance with the provisions of section
677l of this title, so as to effectively terminate Federal supervision over said assets, then the Secretary shall proceed to make such distribution in a manner, in his discretion, deemed fair and equitable to all members of said group, or convey such assets to a trustee for liquidation and distribution of the net proceeds, or convey such assets to the persons entitled thereto as tenants in common.