with less than 5 years left the total amount he pays in interest might be less than the standard dect.
That is true on the existing loan, but not on the refi should he choose to go that route. That's why I think having only 5 years left is not as good as having 30 years left.
You have someone else's money for 30 years instead of 5. At an effective real interest rate of zero the entire time instead of five years at 5% or so. This is a very easy decision. The only complication is that it does tie you to the property for 30 years, but renting can be lucrative.