You can't usually soft boot your machine with CTRL+ALT+DEL while A-10 is running. But if you have a bad mission and don't want to the results to be saved, there is a short period while the next part of the program is loading when you can soft boot.

So to stop the mission details being saved, press CTRL+ALT+DEL as the next section is loading. When the game is restarted, the mission details will be gone.