Will WalMart fail but be replaced by manufacturers selling direct to end-users and disintermediate Amazon? I have no idea, but it's no less plausible than Amazon driving absolutely everyone out of business.
Seems unlikely, because the main reason to go to Walmart or Best Buy is to get the product the same day you want it, and also to see it in person before buying it. Amazon won't drive everyone else out of business until they offer both of those.