If you destroy the command center then alt-F4 it loads the most recent autosave.

but whatever.

It is challenging, but I wouldn't call it Iron mode. That would be where you start the whole campaign over again if you lose a mission. I just had to restart a mission on the final swarm because the infected broke through one of my outer walls. If they were one layer thicker then there wouldn't have been a problem. But I'm not complaining, since a mission plays out a bit differently each time. You do things in a different order, put things in different spots etc. The game is no so linear that you repeat every step exactly. Plus, your command center being lost is only the end result, the mistake you made may have been in the first five minutes. In my case I lost the mission as a result of not putting up enough sawmills early in the mission.

Sounds like you need to lower the difficulty if you are having issues. Get to the point you win with no problems, then increase it.

there is a way to manually copy the save file, to do the troublesome manual save