Two rooms (location numbers 0x39 and 0x3a) exist but are normally inaccessible. When reached (requires hex editor), they display hidden pictures. Pictures are here:
One text (index number 0x92) exists that is never displayed. It says "Brian Fargo
If you complete the game by saving Wing, he mentions that he saved your life in the Koranth cave. However, the cave has two paths in it, only one of which is essential to complete the game, and which does not involve Wing at all. The other path, where Wing saves your life, is optional.