(a) A valid agreement made by a testator to convey property devised in a will previously made shall not revoke the previous devise, but the property shall pass by the will subject to the same remedies on the agreement against the devisee as might have been enforced against the decedent if he or she had survived.
(b)
(1) However, a contract to make a will or devise, or not to revoke a will or devise, or to die intestate, if executed after June 17, 1981, can be established only by:
(A) Provisions of a will stating material provisions of the contract;
(B) An express reference in a will to a contract and extrinsic evidence proving the terms of the contract; or
(C) A writing signed by the decedent evidencing the contract.
(2) The execution of a reciprocal or mutual will does not create a presumption of a contract not to revoke the will.