Well, you could disable all the esp files and remove any textures apart from _land_default. I'm not sure if Morrowind copies any meshes to the hard drive; they should all be included in the bsa archives, though.
And no, it wouldn't give you your original exe back. Most patch programmes create a back-up file, though. Are there no files in your Morrowind folder called Morrowind.exe.old or something else along those lines?