Bug, not a feature
The self-destruction "feature" is familiar to poor sods using Lotus Notes for email; indeed screen grabs may be the only way to keep an email indefinitely, since no-copy also means no-print. In practice it becomes a bug when somebody sends a self-destroying email that contains information that is needed for future reference or subject to a legal retention requirement. I'm not sure that the "GMAIL ate my homework" argument is going to work in court.
I think that old email from Google about "don't be evil" has self-destructed.
Biting the hand that feeds IT
