Per Mike, from their forum:
"Ill shed what light I can for the moment. truth is, I dont know the whole story yet. basically, we were offered summer slaughter and I knew I would not be able to do it, but I didnt want to deny captain chris the opportunity, so I told him if he wanted to get it going, go for it. Other than that, all I know is what all of you know. If thats true, its awesome. Me and captain will be meeting up soon to discuss whats going on, so when I hear more, I will pass it one."
IMO if Mike isn't on the tour, it won't be the same. Ruben is obviously the better vocalist, but if not for Mike, this band would have been dead since 2002.