It seems likely that C++ will end up in a similar place as COBOL or Fortran, but I don't see that as a good future for a language.

These languages are not among the top contenders for new projects. They're a legacy problem, and are kept alive only by a slowly shrinking number of projects. It may take a while to literally drop to zero, but it's a path of exponential decay towards extinction.

C++ has strong arguments for sticking around as a legacy language for several too-big-to-rewrite C++ projects, but it's becoming less and less attractive for starting new projects.

C++ needs a better selling point than being a language that some old projects are stuck with. Without growth from new projects, it's only a matter of time until it's going to be eclipsed by other languages and relegated to shrinking niches.

It will take generations to fully bootstrap compiler toolchains, language runtimes, and operating systems that depend on either C or C++.

Also depending on how AI assisted tooling evolves, I think it is not only C and C++ that will become a niche.

I already see this happening with the amount of low-code/no-code augmented with AI workflows, that are currently trending on SaaS products.