Even in that case it's easy to expect the Typescript compiler to remain in existence for its language services (such as intellisense) alone. (Just as Typescript is already used in "salsa" mode by many IDEs/Editors for providing language services for non-Typescript JS code today.)

That said, you would expect more of a middle ground like Python where Typescript type annotations become syntactically valid in ECMAScript but with no clear semantics at runtime, and Typescript would still be needed to compile/verify type assertions.

There's also the case that transpilers will likely remain test beds for both future features for the language and supporting complicated backwards compatible scenarios.