I think, if CN wants Toonami to not die within a month, they shouldn't just bank on nostalgia. Instead, they'd do well to adopt the following model.
Use Adult Swim to premiere new anime (or rather newer anime). For Toonami, use it to show off retro-sci fi anime. Stuff like Macross (or even just Robotech, if they wish), Legend of the Galactic Heroes, the good Gundams (UC shows, not that Wing/G/Seed AU stuff), Gunbusters, stuff like that. Having a few classic toonami shows is fine, but it shouldn't be their entire lineup
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"One of these days, I'm gonna find a loophole my friend." - Man in Black