Lots of folks innocently suppose that "Microsoft Windows (and the type of computers it runs on...) is 'It.'"
They say that because this is the only type of computer-hardware that they know.
But the "real world" of computer hardware is vast, ranging from the very-largest machines to the tiniest. Microsoft Windows, in all of its glory, runs only on two-or-three of those.
Linux, on the other hand, runs on everything.
This means that Linux is already enormously important, because it is a cooperatively-developed operating system. Lots of folks have a business interest in making the system work in more-and-more situations, and "a rising tide lifts all boats."
This does not mean that "Windows will go away." (Frankly, in the real world of computing, "nothing 'goes away.'") After all, the important thing about any computer system is not "what it runs," but rather, "what it does."
So... "be prepared." Be flexible. See the "big picture."