I think you're misunderstanding both the attack and full-disk encryption. The decryption key is not in RAM every time the machine starts; you have to enter material to derive the key at bootup. And the attacker does in fact have minutes to recover whatever's in RAM once the machine shuts down --- which means that if you shut your machine down before leaving the office (which you have to do), remanence simply isn't a threat at all.

Everyone "shreds" their hard disk if they lose the password. That is the point.

Also, the Plans are to the Death Star, not the whole Empire.