A couple of months ago, I read an article basically stating that he's back in the band, for now. When he and Jeff were at the airport after the last show on this past tour, he basically told Jeff to go back home, and start writing some songs for the next record, and that he would like to play drums on it. The catch is, that Jeff has to write the songs pretty quickly, because Dave might not be interested in 2004, or so. So it really just depends on how quickly Jeff gets some decent songs written, and when Slayer is ready to get back in the studio. So who really knows what Dave will want to do when that happens. As of right now, it looks like he's back in Slayer for good.
Jeff was the one that initially asked Dave to play on the next record, and Tom and management seem pretty cool about the idea as well. Kerry, of course, is the only one who is lukewarm about the idea. Kerry doesn't like the fact that Dave is devoting so much time to side projects like Fantomas, and Kerry wants Dave to make Slayer top priority, and Dave doesn't want to do that.
I don't think it will make that much of a difference in Slayer's music though, since Dave is involved in none of the songwriting. Jeff does most of the songwriting, and since he used to be a drummer, he basically tells Dave how the beats should sound along with the different riffs. Dave basically adds drum fills to songs, and thats it, so I don't know how adding Dave will really change Slayer that much. Paul was a great drummer, and I don't think too many people were complaining about the drumiming on Divine Intervention, Diablos in Musica, and God Hates Us all.
