Vis a vis deepstrike debates, it's as easy as One, Tsu, Three.
In difficult ground, press on.
In encircled ground, devise stratgems.
In death ground, fight!
--Sun Tsu's The Art of War
Basically, how the devil are you going to disengage into enemy territory, even if it wasn't when you started your attack? You're still going to get intercepted and pounded into rubble. Now, if there's only one hex cutting you off, maybe there could be a random chance of surviving and getting back to friendly space without being intercepted? But beyond that, you're left with being in death ground. At which point you have only one option. Fight.