Next. Assaulting a unit that is falling back. Declare the assault. The unit that is falling back must immediately make a leadership test. If it fails, the unit is wiped out, and the unit that declared the assault does not move. If they pass, they immediately regroup w/o a consolidation move, and the unit assaulting does so normally.
When falling back. The unit falling back must fall back directly towards the board edge. They move over dangerous and difficult terrain, not around it. This means its possible for them to fall back, run over a destroyed vehicle, take 25% casualties during that phase, and would then be required to run another 2d6. Any phase that you take 25% casualties you are required to make a moral check. A unit falling back must always take the shortest route towards their board edge, even if that means running forward and around units. Its only when there is no way out, and they are required to move a distance that cannot get them anywhere that they are trapped and destroyed.