Having recently gone through this, I can tell you that AS is absolutely wonderful about working with you after the passing.
Email
[email protected] and put in the subject:
Attn: memorial miles
Give them a copy of the death certificate as well as the needed AS mileage plan names and numbers for transferring from/to. In our case it was transferred spouce/spouce. No fees, it was done in about 24 hrs.
Again I can not say enough about how good Alaska was to work with.
-beav