I'm not sure what you're implying? That Rob, Jess and Tress can't do those characters justice anymore because I'd have to disagree with that. They've very talented actors who still work on cartoons regularly. I'd hardly consider that live performance their A game or even their B game though Rob and Jess hold things together better than Tress at this point. Tress has been phenomenal on Futurama though.
Reviving the entire thing would be rather difficult for many many other reasons. It would be a lot easier to make new Pinky and the Brain or just more adventures of the Warners than to revive every component of Animaniacs.
You could not really hope to make something that was quite the same but that doesn't mean they couldn't make a good show with the same characters and at least most of the same settings.