Even if it is objectively better in every way (not saying it is, only going for the most extreme end point for purposes of making a point) it is not guaranteed to replace C. Too many people have invested too much time mastering C and learning to deal with its quirks to simply give it up.
There may come a day where basically 0 new C projects are made. I do not think that will be in my lifetime. And I say that as someone with near 0 investment in the language but intends to get more serious about learning rust in the near future.
We've already thrown away POSIX compatibility. Linux isn't POSIX. Mac OS X isn't POSIX. Windows isn't POSIX. POSIX only continues to exist in varying degrees at different times.
There may come a day where basically 0 new C projects are made. I do not think that will be in my lifetime. And I say that as someone with near 0 investment in the language but intends to get more serious about learning rust in the near future.