Survivorship Deed for Seller-Financed Property

[Rob Young]

I purchased two rental properties from a 74 year-old seller by assuming his existing bank financing. The title is still in his name for both properties; I am simply paying the bank on his behalf. My contract with the seller gives me up to five years to pay off the existing bank loans. Once I pay off the bank loans, I own the properties. 

Given the seller's age, do I need any additional protection, such as a survivorship deed, that will ensure that the contracts remain in force even if he passes away prior to me paying off the bank loans? 

Any suggestions for how I can protect myself?