Quickest way to get from La Roque -Gageac in Dordogne to Nice?

It is long so i suggest you try www. Viamichelin.comwebsite so u know your options.
More than likely it is a drive to a major train hub southof the dordogne then straight train to nice.

Chris, You should be able to answer these questions using viamichelin.com for driving times, and rome2rio.com for bus, train, and flight information.

It takes about the same amount of time no matter what mode of transportation you choose, with the exception of driving to Bordeaux (2:40 hours driving) and flying (1:50 hours), not counting the waiting time in the airport.

Other possible airports, Toulouse or Sarlat, require plane changes in Paris. Leaving from Sarlat, a couple of the itineraries include plane changes in Corsica, which would be different.
To double check flight possibilities, try skyscanner.com.

Is it a reasonable day trip--meaning a one-day trip, I assume--depends on you and how much you enjoy driving. Viamichelin says 8:41 hours (half of that on freeways). add in your stops, and count 11 hours. Have you thought of leaving late the day before, driving a few hours and stopping for the night. At least you'd arrive fresher for this family member.

Yes unfortunately the Dordogne is kind of far from any transportation hub, so this is going to be a long trip no matter how you do it.

I just made that drive in June going the reverse direction. Left Nice about 0700 and arrived at Cenac, close to La Roque, about 1630 with about an hour of gas/food stops. I just followed the car gps. That did not match Michelin or Google but we got there in about the same time.

Thank you all for the helpful responses. Rome2rio and via michelin are great resources. We'll report back on the journey.