I think the confusion is that there is no "gift" today if you won't see any money until the donor dies. Those are called bequest expectancies, are entered similarly to a pledge, but without and due date. They are also revocable and counted separately from all other transactions.
Here, it sounds like the donor is making a pledge, due in full in 2029. What they have done with the bank is made sure that if they die before 2029, you will still get what is owed by 2029.
I would record this as a standard pledge. If the donor dies before 2029, I would not write the balance off but, instead, pay it off with the realized bequest.
John
John Taylor Principal, John H. Taylor Consulting, LLC 919.816.5903 Big ideas; small keyboard