I posted yesterday that I honestly don't know whether Yahoo! is right or wrong in not providing access to the soldier's emails to his family. Today has dawned, and I still don't know. There are good points on both sides, and all I can really say is "Be careful what you ask for".
Seems to me that his death nullified the contract he had with Yahoo.
Actually, the easiest out for Yahoo is to have someone "leak" the mailbox contents to the family. Blame it on a rogue staffer who has been "punished"(3 lashes with a wet noodle) and be done with it.
1) If the Marine had a will and the executor has properly filed the will, then the executor can assume control of the account with appropriate documentation. I assumed control of my brother's AOL account (although that took some money) and was able to wind it down.
2) If the Marine was intestate (did not have a will) depending on the state, an administrator (usually with the Next of Kin preferred) can be named executor or administrator of the Estate. Then #1 can kick in.
Essentially it boils down to sort of a business proposition. I'd be surprised if Yahoo did not have some policy regarding deceased accounts. An executor/administrator is empowered to act on behalf of the estate of that person which would even include free email accounts.