Comment by tptacek

Systems that lack forward secrecy are by design incapable of preventing archives of eventually-plaintext messages. There's nothing you can do about it; every message you send is irrevocably a part of the adversary's record, and, because you rely on a single long-term key, you know eventually that record will be plaintext. That's why forward secrecy is such a big deal, and why every modern messaging cryptosystem uses ephemeral keys.