The good answer is to only buy stuff that let’s you actually OWN what you put on it. The failure of Nook is only really a problem if they remote delete your stuff (which Amazon has done when they lost rights to stuff, don’t know if Nook has). If they don’t remote delete all it means is that you won’t be able to get new stuff for it, a minor nuisance at best.
Which is of course one of the big reasons I’m still a physical media guy, you always own that.
Calibre lets you strip DRM, make backups, restore to device, convert formats. Very useful app.