Page 20 THE EDGE OF THE WORLD
"The ... battlefield edges... are treated as impassable terrain for making room, recoil, push-back and repulse."
Note that Flee and Rout are omitted from this list, so you can flee or rout over the table edge.
Page 42 LOST AND/OR REMOVED ELEMENTS
"An element is also lost if any of its base leaves the battlefield edge..."