What is the ruling on an agreement between the tenant and the landowner for the tenant to take a portion of the land equivalent to 1/16 of the rented area in exchange for vacating the land, when this was done with complete mutual consent?

The tenant is not permitted to refuse to vacate the land after the lease term expires, even if the law or custom stipulates otherwise, because it is an unjust law. A ruler's judgment, though outwardly just, does not make lawful what is intrinsically unlawful. If the landowner was compelled to agree to the division and did not do so willingly, it is not permissible to take a portion of his land. However, if he willingly grants you that portion without coercion, then there is no blame upon you.