S.B.
My mileage from 1993 was still in my account. Since they merged, I had to manually link it up to Delta for the miles to convert over to Skymiles (Delta's program). I recently finally used the miles. Back in the day, Northwest proudly advertised that the mileage NEVER expires. Not sure if that still is the case anymore.
As to low fares, I sign up to expedia and travelocity's low fare e-mail alerts for certain routes I'm interested in. I also subscribe to airfarewatchdog.com. I've had very good luck with getting great deals through priceline's name your own price for hotels.