As long as you disconnect the receive from the satellite feeds prior to Dish Network sending a kill signal to the DVR then playback functions should continue to work (2+ years for me) - even my external storage continued working, but I haven't tried it in more than a year. I have no idea if DVR playback would continue to work if you were to leave your received "connected" after terminating service. Every few months I'll plug-in my 622s (at least two of them) and watch some old VOOM MonstersHD movies and EquatorHD recordings.
Would you be willing to try it out for those of us that are curious if the EHD still works? I have 10 EHD's of stuff I'd rather not lose.