Disclaimer: I've worked almost three years at Kmart in customer service, since July 2015. So, my post will be somewhat biased.
With that aside, I think Kmart's business model is more sustainable than Sears. Discount chains are still king. They've been able to diversify their in-store selections. Both Target and Walmart have added modest grocery sections. Most of what you can buy at a traditional "department store" as we know it, can be bought at other stores, whether specialized or not. Anything I can buy at Sears I can buy at Target, Walmart, Lowes or Home Depot or Best Buy. Hell, I'd even say a majority of merchandise on the salesfloor at Sears is on the salesfloor at Kmart. That right there is the company's biggest problem; Sears is dragging Kmart's business down. Sears is a dinosaur of the retail industry and it's business models is failing in the "I want it now and cheap" era of consumerism. That's not to say they haven't tried. They've implemented in-store pickup (which at my store is heavily utilized) and a rewards program with actually saves customers' money. Plus, a lot of customers I talk to say they prefer our store's smaller footprint compared to Walmart and Target. But here's the other problem, everything Sears Holdings does, they do it after everyone else has already done it. They've fallen behind the times and failed to keep up with consumer trends. But I reiterate: this is NOT without trying. Sears Holdings is still a company. It exists to make money. Corporate is doing everything it can to make money. They're closing underperforming stores so they can better focus their business, not because they've given up. Wait for a Chapter 7 bankruptcy filing before saying that.