The DVR STB could still play existing already recorded shows if cable goes out. But only as long as the STB wasn't powered down and restarted while the cable is down. Because if you power on a DVR STB after a power outage and the cable connection is still down, it won't come up far enough to play back existing recordings.
direct tv boxes can playback dvr feeds with no sat feed and that is after a reboot as well.
