Ask-Leo.com discussed this very issue, and the conclusion is no. By it's nature Messenger does not store any data, it's all in memory, and that memory get's dumped every time you reboot you computer. No logging mean no logging.

Are you *sure* there's no way to retrieve MSN Messenger history without "archive messages" selected?

In the future if you want to log someone's else's chat even though they know to turn off the logging feature in Messenger, there's several programs (MSN Chat Monitor) that will spy on Messenger for you.