The problem with the dualistic error handling strategy you're proposing is that the "severe" path gets even less testing than normal error recovery schemes do. Imagine you're working with a big non-exceptional C++ codebase (e.g., Firefox) and somebody throws std::bad_alloc. Even if you don't abort immediately and let the exception unwind the stack, the unwinding process will still leave lots of invariants broken, since all the cleanup paths are wired to return codes and will not run on unwinding.

The result is that your program can be almost arbitrarily broken after throwing. You might as well have just called longjmp.

It's because unwinding in only rare cases often produces bad results that I favor making unwinding the only error-reporting machinery in a language. If you use exceptions to report all errors, everyone starts caring about exception safety again.