War in heaven...help me out here peeps?

I’ve been thinking about this for years now….the war in heaven. Did Satan really think he could overthrow the lord? I know he has a huge ego but seriously. Also it goes on about the war between Michael and Satan, they cant kill each other so why fight? Can angels die? In the film dogma it says that if they cut off their wing they can be killed as they become human…but then they would still end up in heaven right. I am confused