Gotta agree with Chuut on this one. The planet is still in ISC possesion. As the mission occured on said planet, and there is no Alliance base adjacent, he should be able to disengage. In fact, the ISC planet would help him out by using it's sensors to lend ECM.
This sounds reasonable to me in regards to the ISC. They can evade due to good sensors. Roms because of cloak. Other races however should not be able to, allthough the planet will not be detecting them, the fleeing ship will not be able to detect other patrols and therefroe would be trapped unless killing the opposing ships.
This is at least what I personally got from reading this rule.
So Chuut (as ISC) would have been allowed to disengage on an ISC planet regardless of surrounding hexes. Most other races would not be able to.
Anyways
Nemo's ISC CAY dies to a suicide shuttle launched from my Lyran/Klingon Jagdpanther CL, Matsukasi in his L-sCF took the bloody nose (as is his trademark)to aid in the kill