check out a script called morphix for reordering: http://www.scriptspot.com/3ds-max/scripts/morphix as long as you still have a version of the mesh with the original vertex order, it can copy that over to the mesh with the mangled one. i don't think there's a manual way in max. btw. if you have access to maya you might…
Better thing is to adjust your workflow to avoid this problem. Reordering vertices is a time-consuming and error-prone job. But if you're stuck, check scriptspot.com for tools.