I have the Empire Remnant Isolated to Yag'dhul.
I tried using an all stealth raid as Pentastar.
The game declares "Invasion Commencing", the lightsabers flash by the planet, my heroes disappear, Isard disappears, menu shows she is still alive as leader and I am stuck.
Will try using a regular invasion, but I was trying to save as many heroes as possible.

UPDATE: Even with space fleet cleared out, normal invasion force, the same thing happens, and it is impossible to defeat Isard.

UPDATE2: After defeating Maldrood and incorporating, Yag'dhul revolted,and Isard appeared with her fleet complement at Kessel.

UPDATE3(not that anyone seems to care):With a Spy Network hero, I can now see the Isard era heroes are also in the Maw.