I submitted this question to FFG support about the rules and got an answer. I'm posting it up here so it gets saved.

question: Can a cloaked unit withdraw to the space that the battle took place in if all the other units were destroyed leaving that space empty?

Answer: No. The units must withdraw to a different space.

I hope that this answers your question!
-Corey Konieczka
Fantasy Flight Games
Design and Development