Retreats- Retreating "forward"

[Yoper]

Q: Can units in a "out of supply" territory attack in conjunction with units from outside of the pocket and then after one round of combat retreat to the "in supply" territory?

The old A&A retreating forward trick. 

This isn't just about out of supply units, it could just as easily apply to any situation where there are attacking units on opposite sides of the defender.

[Mark]

Unit can retreat in the manner. Units must be retreated to a space that was friendly owned at the beginning of the movement phase.  The scenario you outlined happens often - where the cut off units retreat through the encirclement back to friendly lines.  I can see why you might not like it (until it happens to you  )  but, I think allowing it to happen is important.

There were a lot of instances of units breaking out of pockets and making it back to friendly lines - even big corps sized formations - so it is not entirely against historical precedent.