Dish will activate it as an HD receiver but it will only receive the original MPEG2 channels. They would be paying the new price for the hd package though.
My 811 is packed away in my 622 box, I was wondering the same thing. Not worth selling at this point. Will probably just keep mine for a backup receiver.
I think they will still turn on HBO and Showtime on an 811. Even if they wouldn't it still works for SD and local OTA. Dish wants it back so they can redeploy it as a 851. If you have the new HD pack you can use it as a secondary reciever and get the mpeg2 channels.