No grazing or recreational lease shall be for a period longer than 10 years except that when the recreational use is combined and is incidental to residential use on the same parcel, and the lease so recites, the lease shall not exceed 50 years. The lessee shall be notified by mail of the filing of any application to purchase the leased land or any portion thereof. The lease shall terminate as to the whole or the portion of the lands described therein on the date the sale of the whole or of such portion of the leased land is approved by the commission. The lessee shall be notified by registered mail of the termination of the lease as to the whole or portion sold. As to the portion of leased lands not sold, it shall be the option of the lessee to terminate the lease, or to cause the lease to be amended for the unexpired term, at the same annual rental per acre, without the payment of any additional fees.