I played four games; in each scenario I chose to "lie down and accept death". The only one I didn't survive was when I forgot how to breathe. Seems like the AI has a bit of a savior complex :)
You can pay alone, no problem. Though it's obviously more fun with people. The AI is pretty arbitrary and there are many ways to cheese the scenarios. I think that adds to the fun though and it's best played with people just trying to have fun and not super pressed by wanting to win.