I'd like to recommend you to switch to Hitpoints by Numbers in Graphical options menu - that will clarify this situation.
The idea as follows: after you've issued some move&fire commands you may cancel some of them in case you see a mistake (this feature prevents you from reloading again and again). To make it more usefull the game lets the player to overkill (deal more damage than hitpoints) a unit to cancel some fire commands later. It also allows you to redirect your fire to another target. All fire and move commands can be cancelled untill you've hit "End Phase" button.
The remains of a dead unit occupy a hex till the end of turn. That's because we'va united "Move" and "Fire" phase into one to make the game faster. So the units are destroyed after all movement is done.
I'll attach 2 replays of two different ways to complete The Stand... in 20-30 minutes
One more thing - you get resources only if you fully control the territory. Here are the replays.