I'm not sure if this is a bug or not. I wanted to see what happens if my HQ gets damaged five times, so I started a mission then immediately abandoned it five times.
In the mission where my HQ dropped to zero, it said my HQ was overrun, but the mission did not end. I could not move my exo, I could only rotate it.
So, I abandoned that mission, and it took me to the map screen. It said "HQ Overrun" in big font, but the game did not end. I had to quit to main menu to get out.
Is this as designed? It seems kind unfinished that the game doesn't really end.
