Here is what I know about UA's policy:

UA has a correct politic for the surviving partner too - which makes - economically (and if you want to have a merry widow) lifemembership attractiv.

From Silver Wings FAQ:

"My spouse had a membership, but he/she has passed away. Can the membership be transferred to me?

Yes. Silver Wings Plus must have a copy of the Death Certificate, name, address, date of birth, Mileage Plus number and a letter requesting transfer of the membership. The surviving spouse will be issued a new membership card with his/her name and Mileage Plus number."