It would take some time to fill the void. The Wal-Mart behemoth wasn't built overnight and if it was easily replicated their competition wouldn't be lagging so far behind. I know I would miss them if they vanished tomorrow, and I'm sure the 100 million people that shop there weekly would miss them as well.
It might take a month or two IF they all disappeared overnight. Hardly realistic to assume they would though.
We are witnessing a downturn in Walmarts dominance, leading to more competition, which is a good thing.
Now, you may hold some personal fondness for Walmart. But I seriously doubt most care what name hangs over the door. Their only concern is, someone is there to sell goods at a price they are willing to pay.