Reasonable if you ignore maintainability and standards compliance.
Not a coder, but if you used an idiom that worked because of a compiler quirk then that could lead to problems down the line but related to maintenance per se, hence why I added the second part.
In any mission critical situation the entire tool chain is just as locked down and controlled as the "source code," even down to the silicon.
the ISS laptops run on commodity hardware and software, often undocumented, and from my interview with that team the notion that they have some fully deterministic system set up for their operations is horrendously false, and they've run into many issues because of it
I doubt NASA would ever ever upgrade compilers on software once tested. If it is like a aviation, there might even be manual passes over the assembly code for further verification.
I was thinking in a historic archiving sort of situation, bringing to mind recent stories of NASA code being unearthed. Basically I was expecting "it passes all the current unit tests" to be an insufficient standard for NASA coding.