The death of the lender is not a risk to the borrower because he gets the signature he needs before any money gets deposited into the contract address

The signature is created by the lender in advance and shared with the borrower, and it is valid for any transaction that meets these two criteria: (1) it spends the utxo the borrower intends to deposit into the contract address, which the borrower tells the lender when he accepts the loan offer (2) it sends the lender an amount equal to the principle plus interest

So if the lender dies mid contract it has no effect on the borrower. He can still pay off the loan using the signature he already has, and send the collateral to himself. If he uses the signature he already has, the transaction will be valid as long as the transaction also sends the principle plus interest to the now-dead lender (which is exactly how it should be -- those were the terms of the original agreement, and bitcoin doesn't know the lender died)