Lucas has done everything he could to make sure the original would not be re-released. He hates them with a burning passion for some reason, and frequently insists that the redone versions were his 'real' unrestricted vision; even though the only differences are ridiculous things that have no real merit.
According to popular theory, when Lucas released the special edition he did the cuts and edits to the original negatives, making it impossible to use them. This leaves only the Library of Congress versions of the original film in tact, and I don't see Disney going through that much effort.
About the only way to see the original is to hunt down a VHS; if Lucas hasn't destroyed them all with a chainsaw.
that is untrue that he destroyed them. not to mention when he made the SE they had to make digital transfers of the films so those original unaltered transfers still exist and we know they still exist as from special edition to special edition he has changed some of the things bakc and fourth.
Plus as others said they did release the originals on DVD once already