> I honestly think it's more likely that some part of the Web Components tech stack will be removed from Chrome, Safari, and Firefox in the next 20 years, consequently breaking apps built with them

That already happened.

HTML Imports got deprecated (in favor of a JS-only solution), though Firefox already implemented them.

Custom Elements v0 was deprecated even though Chrome implemented it and hastily re-wrote Youtube with it. They had to wait ~4 years to remove the implementation because it took Youtube that much to switch.