An update to this story on http://avherald.com/
"On Nov 27th the FAA released transcripts and audio recordings revealing, how air traffic control tried to raise the crew and how the crew finally reestablished contact. According to the transcripts the crew was handed off by Denver 28R/28RA to Denver Center 132.17, acknowledged the hand off at 23:57:01Z and was not heard anymore until 01:14Z, when the crew reported again at Minneapolis 13D.
An e-mail supposedly written by a friend of the captain on flight NW-188 says, that the captain had left the cockpit to use the restroom, when the first officer received the last frequency change (see Denver position 28RA) and selected a wrong frequency. He never got a reply on the new frequency, which actually was in use by Winnipeg in Canada. When the captain returned, the first officer did not report the frequency change. ATC chatter could be heard in the cockpit, so that the captain never had the idea they might not be in contact with ATC. They entered a discussion about the crew rostering and used their laptops for about 5 minutes. With a tailwind of about 100 knots they were faster than anticipated. When the flight attendant asked via interphone, when they would arrive, they checked with their navigation display, set at full range 320nm, and found themselves overhead Minneapolis, on reducing the range they identified their position at Eau Claire. Their ACARS did not have a chime, but a 30 seconds light to indicate new arriving messages. The crew had tuned 121.5 MHz, but may have turned down the volume over disturbing chatter. The captain is not trying to appoint blame to others, but to explain the events on board of the aircraft and takes full responsibility for the events."