That scenario is not really any different from having a technology advanced country (like the US) alongside some underdeveloped nation. The US could, in theory, close its borders and produce everything it needs itself, and leave said underdeveloped nation without the benefits of, for example, Netflix, Nike & Nvidia.
But it won’t, it’s not economically efficient. Economic theory (of comparative advantage) tells us that there’s always something that the less developed world can produce relatively cheaply, in exchange for sneakers, streaming services, and G-force Now subscriptions.
Well ya, if you don't need labor, why keep 8 billion laborers around polluting your planet?