I'm not quite sure what you are talking about, but I think it an assault. If it is an assault, it will take a couple of turns to play out.
So here is what I think you are trying to describe:
- A stack assaults another stack (whether by normal or extended assault is irrelevant).
- All attacking units are disrupted or demoralized in the assault by defensive fire. The attacker's turn is done, they can do nothing more this turn.
- The defenders do not assault the original attackers this turn (again why is irrelevant), but they might have been able to.
- The next turn the original attackers retreat from the hex before the original defenders have activated. Whether demoralized units failed to rally, or disrupted and good order units chose to leave is irrelevant, the hex is vacated.
- The defenders now get a parting shot at the original attackers and the original defenders may still activate and do whatever.
It seems that you think all that can happen in 1 turn, it can't, it takes 2 turns. You also seem to be under the impression that units may move between assault hexes, again they can't.