Why would LEGO care whether any third-party stores (i.e. competitors of LEGO's
PaB website) close down?
Also, third-party stores would still be indispensable, because there are so many
parts that are unavailable from the PaB website.
When taking over bricklink, LEGO claimed they wouldn't interfere with the
marketplace, implying they wouldn't compete with sellers. If they want to
compete with sellers, then many sellers will leave and move to the independent
marketplace.
They would also need to behave like other BL sellers. I'd leave them negative
feedback unless they improved their order turn around times.