Lots of blind people here trying to describe an elephant.  I had a client die recently, a month shy of her 100th birthday.  She owned a highly-appreciated portfolio of stocks, that will get stepped-up basis.  But until a few years ago, 25% of it was in one company.  She sold most of it, and it has since gone down more than 50%.  Her kids are happy she paid the capital-gains tax, rather than leaving them with stepped-down basis.

What's his tax bracket without the gain?  If he can spread out the gain at, for example, $25,000 a year for the rest of his life, will that even be taxable?  Is he reading the same news as you and I, about how Congress might repeal stepped-up basis?  (They did it once already, but quickly changed their mind.)  Does he have ten grandkids, all of them in lower brackets so that another $5,000 a year in LTCG would not put a dent in their 1040 refund?

How much in property taxes is he paying on this unimproved land?  Is he "dirt poor" -- too many assets in real estate, not enough cash in the bank? If he needs $50,000 a year for assisted living, would the land payments provide that tax-free because it would be offset by medical deductions?  

The factors in favor of a sale probably equal those discouraging it.  What you can tell him:  1) Get a big enough down payment that you make money even if your heirs must foreclose.  2) Don't be surprised if that note gets paid off early, when the buyer has permanent financing for the Amazon warehouse they expect to build.