C will end when our entire technological civilization collapses and has to start over from scratch and even then after a century of progress they will invent C again.
A while back I wrote some C code to do the "short-bread" problem (it's a bit of a tradition at work to give it to people as their first task, though in Python it's a lot easier). Implementing a deque using all of the modern guard rails and a single file unit test framework still took me a lot of attempts.
Nowadays, not so much. Computers are multiple orders of magnitude faster, have multiple orders of magnitude more memory and storage and do things multiple orders of magnitude more complex than they used to. Portable assembly still has its uses obviously, but safer/easier/faster alternatives exist in all its niches.
C is much closer to any other high level language than it is to assembly. 'Portable assembly' might have been true with trivial C compilers of the 70s and 80s, but not with compilers like gcc or clang.
And C is still the best way to talk to the hardware in a portable way.