Parents Want To Put A Lean On My First Home After Offering To Help Me Financially.

Lien* So I just purchased my first home. My parents gave me money towards the down payment and about $15,000 extra for updating and repairs, which they want back. The agreement is to pay them back when I decide to sell. I got an amazing deal on this home and it’s worth about 2x what I paid. I have no problem with this agreement however, god forbid, what if my parents pass away before I decide to sell, and I still have a lien on my home? Does this just go away? Will I not be able to sell? I am completely clueless on how this works. My parents are up in age and I just to not want any issues for either of us in the future.