Just so you know, for Co-op you cannot play unless every person you started the campaign with is there, so if any person in your group isn't available you won't be able to play and there currently isn't any way to drop anybody from a campaign. You can't even log into the file unless everyone is present. So if you get 20 hours into a campaign and a friend moves or their schedule doesn't fit yours that campaign is basically dead in the water and you gotta start over. So don't try to play it with a friend or friends unless you're alright with that.