I recently e-mailed BA, CO, DL, HH, and MC to ask them if a member's mileage/point balance are transferable to a non-spouse in the event of a member's death. So far, I've gotten responses from BA and MC. Here is what they said:

From BA:
We recommend making note, in a legal document, who you wish your miles to be transferred to in case of death. The beneficiary will then need to send in a copy of the death certificate and the document to receive the miles in their account. The beneficiary need not be a current member, however they will need to enroll before a transfer of miles can proceed.


From MC:
Thank you for contacting our Guest Services Center. Points accrued by a Marriott Rewards member are for the member's benefit only and may not be transferred to anyone. Points are transferable to a legal spouse only in the case of documented death of the member. Points are not transferable to another person for any other reason including divorce or inheritance. Please let me know if you have any further questions or concerns. Thank you for choosing Marriott Hotels, Resorts, and Suites when you travel.

I hope this issue carries some interest with yall.