Well in theory, if it fell out you wouldn't be able to shift into low. The crawl box only contains 1 roll pin. Take your shift boot off, and then undo the 4 bolts holding on the shifter. The first thing you will see is the shift block. If it's sliding around on the shift rail then take that roll pin and tap it back into the hole.
I can't imagine how that would've fallen out. They fit pretty tight... If it slides back in too easily, then you need to come up with a new solution so it doesn't happen again.
