My choice would be Steve Warner.
It wouldn't surprise me to see the network pluck some podcaster out of relative obscurity. They could probably get some talented podcaster and pay him/her a quarter of what they pay George, at least initially. And as someone else pointed out, there's a chance they might drop the current format, anyway.
If they want to get a proven professional, how about Frank Morino who does the "Other Side of Midnight" show on WABC? I assume he's still doing their overnight show, I haven't listened in at least a year. I heard some of of his early shows where he interviewed C2C style guests, he was easily better than George.