I see a lot about source codes being leaked and I'm wondering how it that you could make something like an exact replica of Super Mario Bros without the source code or how you can't take the finished product and run it back through the compilation software?
Code can be decompiled, but generally the end result isn't human readable. Just having the decompiler version isn't that valuable. Having the source code as written is more helpful because you get the context of what things were named and how it was organized.
Decompiled code is a bit like reading a book with all the nouns being random letters and verbs being random numbers.
Not completely random, every noun/verb would be translatable to a specific word/name. But also characters, there'd be many characters whose names, intentions and goals, relationships/links would also be in the same unreadable state. The storyline would likely not be chronological, but several actions and decisions by all kinds of actors would intertwine. It would be very hard to translate into a readable story, let alone so that it makes sense