C? Never. I feel like that ship has sailed, it's too primordial and tied to too many system ABI's to ever truly go away. I think we'll see a lot of Rust or Zig replacing certain popular C programs and libraries, but I don't think C will ever go away.

C++ on the other hand? Possibly, though I think that it's just as much because of the own-goals of the C++ standards committee as it is the successes of Rust. I don't really consider Zig a competitor in this space because if you're reaching for C++, you are reaching for a level of abstraction that Zig is unwilling to provide.