I still do believe DBZ will be back. Honestly, Naruto's proving that "classics" will pull in ratings. It's proving that uncut runs, classics and long shonen can pull in ratings. DBZ could do that too, however, unless Funi creates better masters, we would get the Singles footage that was ran on 4/1. And I don't think the Saiyan Saga would be played, either versions. Ocean Dub version just wouldn't fit on Adult Swim Toonami and would only be aired for pacing convience, and the uncut versions...well that's a pacing inconvience.
Unlike DBZ, Naruto hasn't been nearly as overplayed on the original Toonami as DBZ was and it hasn't been on the air in years prior to its return to Toonami. I could see uncut Kai working a bit better than uncut DBZ just because it wouldn't drag out as long, but even then, I'd still prefer for Toonami to not rely much more on the nostalgia factor of their biggest hit and keep getting new shows instead. While DBZ in any form is bound to get good ratings, plenty of other shows need more exposure than DBZ does and they do need to rely more on new content, rather than old, to keep the block going.