If you are a member of an airline rewards program, take a look at the fine print of the program's terms and conditions. You will most likely find language to the effect that any accumulated points are not transferable on death. However, that might not actually be true.
Airlines are eager to sign customers up to rewards programs. For frequent travelers these are often great deals, as they can often get free or reduced cost airfare, especially if they fly on the same airline repeatedly. There is a real monetary value for the account holders. Nevertheless, not everyone uses his or her accumulated point balance before passing away. Since the accumulated points do have a real value, the question then becomes whether or not they are part of a decedent's estate.
The answer to that turns out to be no, unless an airline decides to make an exception.
Time recently reported on this issue in an article titled "What Happens to Your Airline Miles When You Die?"
It turns out that while most rewards programs have an official written policy that points are not transferable on death, in reality most airlines will make exceptions to that policy on a case-by-case basis. If the points are bequeathed to someone, most airlines are willing to transfer the points upon receiving proof of death and proof that the person asking is the appropriate beneficiary.
This practice is discretionary, however, and the real key to getting the rewards transferred appears to be to ask nicely. Airline employees are not required to transfer the points, but if the beneficiary is nice they normally will.
Reference: Time (July 31, 2015) "What Happens to Your Airline Miles When You Die?"