*raises hand* I, for one, don't think Frank should come back. He's moved on and found his niche elsewhere; don't take him out of that niche just because you want Piggy, Fozzie and the rest of Frank's characters to be the way you remember them/you want them to be.
And in that same vein, give Eric a chance. While his Fozzie and Animal could use some work, his Piggy his spot-on. He wouldn't have been given Frank's characters if they didn't think he could handle it or do a good job.
EDIT: And now, having seen the last half of tonights AFV, I'd have to say that Eric's Fozzie is coming along very nicely as well.
-Kim