By what possible metric could you consider C++ "mostly dead"? I'm fairly sure that most, if not all AAA games nowadays are coded in C++, for example. Never mind such little known projects like GCC, Qt, and LLVM. It's not a language I care to use, but it's clearly still very healthy: widely used and regularly updated.
I am sure I saw its corpse on the road.
I kicked and kicked and it would not get up again.
Not to mention that it's "influential" mostly by providing examples of what not to do in a sane programming language :-)
Most programs you use and internet infrastructure are written in C and C++. Furthermore, it's actively used to develop new software everyday by most large companies.
I'd say your first comment is very true and your second is very untrue. There will be sectors that will generally gravitate to c/c++, and a huge boatload that won't touch them with a ten foot pole. Corp languages are jvm based, .net based, js/ts, and maybe Go in some contexts now. None of the companies I've worked at in like 15 years has decided to create new c++ projects (clearly subjective view).
None of the other programming language compilers in the world would not build anymore if C++ would be dead or dying.
There’s significantly less interest in implementing the next version of C++; Apple and Google don’t care about it. So someone’s going to have to update g++ and clang.
While many compilers are originally written in C or C++, most are soon rewritten in themselves.