I like to keep that one handy, too.
If I may Captain Obvious, several folks need federal prison sentences in excess of 40 years.
20 years ago chat rooms were forced to keep at least a year of chats because many hackers would go online to brag after a DOS attack (for example). The carrier will have back ups, the NSA would have them. If they disappeared at the NSA, find the access logs, last person with access before disappearance goes to prison. Or at least let the prosecution begin there.