NPM currently doesn't provide a standalone distribution as far as I can tell, but presumably they would offer one if they no longer had the luxury of being bundled with Node.
Since changes generally don't happen overnight I would expect a transitional period where Node still bundles npm-cli but npm Inc has the time to prepare a standalone distribution before yarn replaces npm-cli. Additionally downstream channels could decide to provide legacy packages containing both.
But that would break 7 years of documentation and tutorials, likely bad for newcomers and thus the ecosystem