These are still very niche languages. Go has a better shot, albeit still long, with the weight of Google behind it, but there is an unbelievable amount of inertia. Rust certainly hasn't replaced C/C++ to any real degree yet.
Maybe time will tell, but I'd lay money that there will be a lot of people still working on C, C++ and Java codebases in fifty years, just like there is a boatload of COBOL and even MUMPS software still out there in the wild today.
I'm not saying that these languages have replaced their older versions, but that one would be crazy if given the choice to choose to do Java/C/C++ for work :)
Maybe time will tell, but I'd lay money that there will be a lot of people still working on C, C++ and Java codebases in fifty years, just like there is a boatload of COBOL and even MUMPS software still out there in the wild today.