I'm pretty sure it's not. Maybe you wish it was, but it's not. C is still commonly used as a "lowest common denominator" language, and other languages often use bindings to native C libraries. This is still very common, and well supported in almost all modern languages (sometimes even completely embraced by some implementations, like cpython). Even Signal has official C bindings (libsignal-protocol-c).
To reiterate my point, one may hope that C goes away, but objectively, in the foreseeable future, it continues to be a backbone of most software.
Rusts ABI may as well not exist however. Rust can co-exist with C. Everything else that depends on C's ABI won't be able to play nicely with Rust without significant work from one side or the other.
To reiterate my point, one may hope that C goes away, but objectively, in the foreseeable future, it continues to be a backbone of most software.