In Black Lotus Party mission, the exit tiles are on the roof, but you start downstairs.
The mission description does warn of a lot of close quarters combat and the mission being indoors, but says nothing about the chance of aborting the mission; the briefing has a regular text on aborting the mission.
I'm not sure if there is any meaningful explanation for this (and I suspect the reason is that defining the exit tiles this way was just easier). The agents land with an osprey in the garden, walk in through the front door, get ambushed, the doors are now locked, and they have to be evacuated though the top floor?
I think it would be fair to warn in the mission description and briefing text that it'll be difficult or practically impossible to abort the mission. Or give some other in-game explanation on how your guys ended up on the ground floor while the escape is through the roof. Or change the exit tiles or start location.