Dancing Hoskuld
Deity
...- did it already have the military instructor when you captured it ....
Currently all great people remain in a city you capture. You will often find a GG in the capital of an AI player when you conquer it. I am thinking/designing something else to do with those GP. EG If it is not the last city many will evacuate to another city with the Great Military instructors forming the basis of the combat units of the retreating army.
This is something I need to do for the settled slaves. The buildings don't survive the attack at the moment but if you aren't running slavery and capture a city with slaves then they should be freed.