State law prevails in a situation when the Buyer in a Land Contract dies before the completion of that contract and has not made a Last Will and Testament.
Absent language in a Land Contract to the contrary, if a Land Contract is signed by a vendee (buyer) who then dies before the terms of the contract are complete without a Last Will and Testament in place, the estate of the vendee has the right to enforce and enjoy the balance of the Land Contract — but also has the obligation to continue to meet the obligation required by that Land Contract (i.e., continue to make payments, perform other requirements).
The question of “who is the estate” of the deceased vendee will depend on state law, as each state has its own laws regarding who is named or appointed as the estate administrator or executor when no Will is in place.
Ultimately, which heirs will ultimately own the land acquired through the completion of the terms of the Land Contract are also set by state law in the absence of a Will. (For example, most state laws provide that without a Will, a spouse will be primary beneficiary of an estate, followed by children, then siblings, etc.)
Finally, the transfer of the property subject to the Land Contract (or the continued performance of the Land Contract itself) would have to be approved or at least considered by a probate court in a probate proceeding, filed after the death of the vendee.
For complex legal property questions such as these, we suggest securing the services of a qualified local attorney to help with Land Contract and probate issues.