Can I abandon an escort mission after evacuating the vip somehow?

I just played a vip escort mission in my impossible ironman and after the vip escaped I was left with the task of killing all remaining aliens, which I abandoned because I had only one sniper at 1 hp left :/

Now I did not get any reward for this mission, is that supposed to be this way? I think it shouldn't since the task was extraction of the vip, not elimination of all aliens?

I guess I wonder: Bug or Feature?

You must fulfill all objectives on a mission in order to get a reward. Once the VIP has entered the extraction zone, the objectives are updated and thus you don't get at reward unless you kill all the remaining aliens.

It's unrealistic that you wouldn't get some partial credit for the mission, but that's how the game works.

That's a feature. Just pretend your soldiers are the ones that have to fly the ship. After all, you wouldn't be playing impossible ironman if you wanted it to be easy!