If it would not shift out of park, it could easily be a problem in the cable linkage and not in the trans. at all. But now there's parts missing, so it's time to get on top of this and figure out what the problem actually is. Post photos like CudaFactHackJob said and try to get an idea what fell out. Check the shift cables, make sure they're intact and move freely when you move the shift lever. Find out what you've got to deal with and then make decisions and move on from there.