aemitch,
My general comment is that you are trying to cover too much ground and will be shortchanged by this itnerary. More below.
As for the question about Lyon to deGaulle, you have two options that are better, I think, than driving all the way back to Paris. Return your car when you arrive in Lyon and then either take a very early direct train to the airport, or do the same the night before and stay at the airport.
There is a small risk that an unusual disruption in rail service could make you miss your flight. If this is unacceptable then I would go with the night-before option.
The train runs direct to the airport bypassing Paris. It takes 2 hours or less.
Your itinerary entails too much time in your car and too little time in castles and cafes and museums. I love the Dordogne but it is simply not worth taking such a big bite out of your trip only to spend a single day on the ground.
Your estimate of only 4 hours to drive from Amboise to Sarlat is not very realistic and if your trip planning is based on similar guesses you are going to feel as though you are always behind schedule.
Is there any chance you could take more time? If not I urge you to cut back and spend a little more time at some of the destinations you already will visit.
Here's an alternative if you leave off the Dordogne: Go immediately to Amboise via train and then execute the start of your itinerary counter-clockwise: Amboise-MSM-Bayeux-Paris. Pick up the car in Amboise and return it in either Paris or Bayeux. Paris will let you catch your breath.
Then take the train to Arles and rent a second car, using it to explore and leaving it in Avignon or Lyon. This plan makes good use of France's super fast trains--much faster than your car--which lets you see and do more.
If the Dordogne is a must-see, consider saving something else for another time.
I hope you have a great trip, whatever you decide!