re3 is a very dubious legal case. They decompiled the game with debug symbols and then did a (aiui) non-clean room reimplementation of the code, based on the decompilation.
It is protected legal activity to decompile a binary and study the source.
It is protected legal activity to study some source code, describe it, and have someone who never saw the source reimplement the code described.
It is straightforwardly illegal to decompile source code, recompile it, and the distribute the recompiled binary.
re3 is somewhere between the latter two, and (again aiui from looking into it 2 years ago) they didn't have a clean room step.
It's probably a good thing no one will litigate it. It seems highly likely to be illegal and reasonably do. It would be a bad thing to spend money on.