Your scenario is based on incorrect assumptions.
A Company Commander does not "authorize" a platoon leader to retreat. There is no "punishment" or "being held accountable" for retreating.
Today's military understands that situations change. An Operation Order (the order to do a mission) is a GUIDE. The saying is "no plan survives first contact with the enemy". An Operation Order will have a "Mission Statement" which is a specific "do this" statement. It ALSO has a "Commander's Intent". The Commander's Intent is supposed to put the mission statement in context. It gives a "why" of the mission, so when things go wrong, the leaders can change the plan to accomplish the INTENT (or overall goal) even if the mission must be changed.
Example: Your mission is to capture and hold Hill XXX until relieved. The Commander's Intent is to provide security for supply convoys going through the area by controlling a key position.
If the unit does some recon and finds out the enemy is on a different hill that can attack supply convoys, the local commander would change the mission and attack where the enemy is actually located. Depending on time and actual distance, the local commander is not going to "ask for permission" and may not have time to fully explain the plan to higher headquarters.
[you can go into all kinds of 'what if' for crossing sectors, but keep it simple for this example]
If the unit is occupying the position and is attacked by a much larger force than expected, the local commander could retreat, evacuate or reposition his unit. He does NOT have to "ask for authorization" before moving. He WOULD report what is happening. If that seems to be a constant of that leader and he is always running away or avoiding the enemy, he would be relieved, prosecuted (unlikely), or transferred to a different position. The Soldiers in the unit would not be "held responsible" for a leader. The senior enlisted leaders would LIKELY be questioned if their leader really was that bad and if there was any way to "fix" him, or if it would be best just to get rid of him.