The reason there are N64 emulators is because N64 code (MIPS 4300(i?) as I recall) is not compatible to the x86 processors. Meaning, no, you can't run N64 games on a PC, unless you either emulate it, or completely rewrite the software running the game. Chances are that writing the emulator is actually easier in the long run...
Think of it like English vs. Japanese. x86 CPUs speak, and read English, and don't know any other language. N64 games are written in Japanese. It's completely foreign to the x86 CPU. That's what the N64 emulators do (well, basically). They translate the Japanese code into something that the x86 CPUs can read and understand.
Does that answer that question? Does that explain how the question you asked is a very unfeasable and unreasonable idea?
Of course, your question was sort of a two parter. You also (sort of) asked if you could "decompile" the ROM. I think what you mean, in this instance, is to extract all of the data contained in the ROM into a file tree system, similar to a PC's file organization system. For that, I'd say that yes, you could do that. However, chances are that the tool made to do this would be game specific, and would require alteration everytime you added a game into the "compatible games" list. Basically, from what I understand, most ROMs don't really have a set file system. So, you'd have to recreate, and decipher each file system as it was given to you.
Of course, I could be mistaken. But, for USFs (Ultra 64 Sound Format), most of them (if not all of them) are in "miniusf" form because it wasn't worth the effort to decipher the file system so that each indivdual sound file could be removed from the ROM. Instead, HCS found a way to catalouge what parts of the ROM were in use while the music/sounds were being played. Then, the USF creation tools basically trim off all of the other unused/unecessary data (or, it's the oppasite. Where it catalouges the areas of the ROM used, and copies those areas to a new file, which essentially is the same as cropping out the uneeded data).
Hopefully this explains why it would be difficult to do what you've asked is possible to be done. Mouser X over and out.