Watauga at Sugar Grove: 92 square miles.
minimum fun flow: 200cfs
Pigeon below Cataloochee: 400+ square miles
minimum fun flow: 400 cfs
I think the Pigeon dries would run twice as often as the Watauga without the dam. In 2009, the Watauga ran 107 days of the year. So conservatively, the Pigeon Dries would run at least 150 days a year, as much as 200 in a good year. 1 hour from Knoxville and Asheville, 5 minute shuttle for class 4. Not to mention awesome big water class 5 with high flows. Everytime it rained big in the southeast, once all the creeks had dropped out, you would have a week of ramping down flows from huge water class 5 to fun class 4 river running, before the next rain hit.
Jocassee and Tugaloo are good options.
If the earth had a soul though, I think Fontana-Cheoah-Calderwood would be top priority. And though there is little gradient lost under those dams, it doesn't take a whole lot when there would be an average flow of 2,000-20,000 cfs. I predict there would be some good river running in there, not to mention an absolutely epic overnight trip. Hike in at Clingmans, run Hazel into the Little T, then all the way down to Foothills parkway, with moving and interesting water the whole way.
Maybe I'd just remove Tuxedo just to piss off the Ashevillians!