My condolences, flying chicken.
A recent issue of Inside Flyer magazine addressed this very issue. It seems DL has one of the more liberal policies about transferring miles to family members after a death. Many of the other majors insist on both a death certificate AND a copy of the will or trust specifically instructing where the deceased wants the miles to go.
The suggestion in the magazine was to include a paragraph in your will or trust covering your wishes for any airline or hotel miles/points you may have accumulated. The more miles and points you have, the more important this obviously is. And if you wish to will your miles to a non-family member, it's almost mandatory that this be spelled out regardless of airline.
Even though most of my outstanding miles are with DL and they CURRENTLY have a liberal transfer policy, who knows what the future will bring. Better to take care of this now and not have to worry about DL changing their attitude at some point in the future.