Even Cobol code hasn't been ported in it's entirety, and the whole codebase at the peak was probably orders of magnitude smaller than C++. It's also far easier to port Cobol - with it being used mostly for data processing and business logic - than C++ that was used for all manners of strange, esoteric and complicated pieces of software requiring thousand to millions of man-hours to port (for example most of Gecko and Blink).

C++ will be here forever, at least in some manner.

edit: spelling