A lease (tenancy) in Thailand is not a real property right (meaning in essence attached to the property as for example a right of superficies) but a personal contract right (in essence attached to lessee). The general rule is therefore that the lease/ tenancy contract ends when the lessee/ tenant dies. It can only be assigned as a contract to the lessee's/ tenant's heirs but this option must be included in the lease, otherwise the owner can take back the property and re-let it as the lease/ tenancy is terminated by the death of the lessee/ tenant.
Contract promise or real lease right
Succession of the lease is under current rent of property laws not a legal right given to the lessee's heirs, such right must be included in the lease agreement as a contract option. However, such option is under current rent of property laws in Thailand not considered a true lease right but a contract promise given by the lessor as a contract party (not not a lease right protected by section 569 civil code), and therefore only enforceable by legal action against the original lessor (continue reference link below).
Death of the freeholder/ lessor
Meaning of section 569, 'rent of property' civil and commercial code
Section 569, part of rent of property laws, protects the lessee in the event of death of the lessor and/ or transfer of the ownership of the property hired. Change of ownership does not terminate the lease/ tenancy. Section 569 only protects the lessee for part of the lease/ tenancy that is considered a true lease/ tenancy right, not considered a true lease/ tenancy right is a succession clause, but also a lease renewal option is not considered a true lease right. Legally/ technically it does not make much different if such clauses are included in the lease agreement registered with the land department or are agreed between the freeholder/ lessor and leaseholder/ lessee in a separate document or addendum to the lease, not registered with the land department. These contract options are in principle not enforceable by or against parties who are not party to the contract.
The lessee is the essence of the agreement, therefore lessee's/ tenant's death does automatically terminate the lessee/ tenancy contract (Scj. 1108/ 1994). This is the general rule, specific exemptions/ protection may apply.