XP use will continue to drop, not because of the planned end of support date (rapidly approaching) but what will kill it DEAD is
Obsolescence of the latest M$ browser that supports the OS.
this is historically what killed all previous M$ operating systems.
Usage will continue to drop as more and more people find compatibility issues that they cannot tolerate but when websites like YouTube drop support for the browser it's over.
At that point remaining users leave like rats leaving a sinking ship.