[Mobhack]

In SP series games an abandoned unit is now a map decoration. It can be destroyed by a unit of yours camping out on the same hex for a turn, but that is the only way you can destroy the decoration. It's built into the basic code that way, and to redo that would mean writing a new game from scratch, where guns and vehicles came as 2 separate conjoined units at the start, infantry as 1 unit.

A decoration has no crew so it is inactive. That is how SP works - the active unit of the decoration is its crew. So if you make an arty unit split and retreat then you do have to pound the ground around the decoration to try to eliminate any fleeing crew.