It will diminish, but never go away until POSIX foundations or graphical programming standards get replaced (most of them defined via C ABIs).
When I was mostly doing C++ and C on day job, 20 years ago, they were the languages to go when doing any kind of GUI or distributed computing, nowadays they have been mostly replaced for those use cases.
Yet they are still there, as native libraries in some cases, or as the languages used to implement the compilers or language runtimes used by those alternatives, including Rust.