Disney's been playing that game for years (since at least Beauty & The Beast; see the ballroom scene), but most notably with Treasure Planet, which featured 2D characters animated over and alongside 3D computer animation (at least one character was entirely CG à la Iron Giant, while another character used CG elements).
As for a comeback of traditional animation, I think that might depend entirely on Pooh's box office success. The Princess & The Frog did well enough, and it was certainly met with enough critical acclaim, but potential doesn't mean successful execution in the long run. I think when people were declaring the death of hand-drawn, they were forgetting that movies can't stand on their medium alone (at least not for long), no matter how impressive -- they need a solid, intriguing premise to back it up, and that was something that so many of those last big flops were definitively lacking, be it via unsuccessful marketing campaigns or their own inherent failings. We can see the same thing happening to all these feature length CG films now, as well as all these other big budget films boasting 3D. Pixar's long-term success, for example, doesn't ride on their mastering of their favorite medium -- it rides on their consistent ability to tell a compelling story. If Disney or anyone else wants to revive hand-drawn animation, they have to (re)learn to start putting story alongside innovation; not after.
I've got my fingers crossed. <3