I had a fantastic time on Sapienza last night playing Hitman. I only have a few challenges left so I decided to strike two birds with one stone - get him to escape in the plane, then shoot it down with the cannon.
I'm not sure what the 'proper' way to trigger his escape was, but I decided to start the mission in the ruins with an assault rifle. I loaded both cannons (wasn't sure which one was needed) and then used the ruins as my base.
From there, it was a matter of picking off every guard I could, until there was about 20 corpses lying at the foot of the steps to the ruins.
He ran down into the lab but that didn't trigger his escape, so armed with some of the guard's heavier guns, I went down there myself and slaughtered absolutely everybody.
That did the trick and he ran straight to the plane, I dashed up to the ruins, and boom.
It was bizarre seeing the level so empty when I went to kill the second target and destroy the virus to finish the level.