What happens when a seller financed note is paid off?

[Michelle Ellis]

I am both a realtor and investor. I have a buyer client who purchased a property with owner financing in order to 'win' against multiple bids.  He will pay the property off in just 3 installments, the last one being at the end of this month.  What happens then?  I have helped folks with owner financed transactions before, but never have assisted someone where they paid it off so quickly.  There is no underlying note, it is a straight owner-finance situation.  

Do we need to have the promissory note released?  How?  Does an attorney draft something that everyone signs?

Thanks in advance!

Michelle, in Leander, Texas