You always need that dedicated Partner on Zombies
But those things that you've stated in your thread, is exactly what pisses me off when they leave...When I go down, I try to recover, not just rage quit, because there is always hope.
My longest run with Zombies was 13 hours straight with my friend.
But yeah, they should add in Solo Leaderboards, I know a lot of people who play Solo and get to high rounds, some people just don't do good with others.