[Imp]

If a unit is immobilised in a position where it can no longer effect the battle just leave it be & carry on.
If your losing more important things, if winning & you want every enemy unit & are doing well easy option if you still have arty available & some form of transport get it in clean up.

Once you think enemy force moral is broken hit it with artillery for a few turns, the crew will bail out and retreat straight into the arms of the unit you sent back to intercept it.