I currently have Cox Digital Cable (with HD). I have a TV upstairs that I just use the QAM tuner on to plug into the wall and get the unencrypted channels.

I am thinking of switching to satellite and canceling my cable service. Will I still be able to pick up any channels (both HD and SD) through the QAM at that point?

Nope. Only works with cable, so you'll need an extra HD-capable satellite tuner for the bedroom TV.

If you're willing to live with SD and downscaled HD on the bedroom set, You could get one of those "dual-tunered" models from Dish, and you won't have to pay anything extra for the tuner and service to the second set.

Well, if the cable company doesn't physically stop the cable connection to your house, you would still be able to get clear QAM in the bedroom.