Our experience was this:

When my ex-wife died a year ago, once things had somewhat settled, I contacted Mileage Plus on my son's behalf (we were both on the line). I'm a 1K, he (was) a 17-yr-old general member. Don't know if these things mattered. They asked that documentation be faxed, which we did. My son received a letter with what appeared to be boilerplate disclaimer saying, in essence, "We don't have to do this; it's not our policy to do this..."

"...however, we have transferred the (~)185,000 miles in your mother's account to yours, and please accept our sincere condolences on the loss of your mother."

...to which we replied with a thank you card to the person who signed the letter. I believe it was a Ms. Rose or Ms. Ross.