My rule is always be within a cab ride of a high stakes flight so I would stay in Paris the last night or stay AT (not near) the airport. One strategy would be to visit Chantilly or Senlis that afternoon, and have dinner and then drop the car and check into an airport hotel (we have stayed at the Novotel and the Hilton; there is also a Sheraton right at the airport but it tends to be the priciest). That way you are right there for your flight home and don't waste an hour getting from Paris (an hour you could be sleeping) . It is easy to be at check in 3 hours ahead if you just have to walk downstairs and get on the intra airport train/shuttle.
We loved Senlis, a delightful medieval town https://janettravels.wordpress.com/2010/06/12/moyen-age-visit-to-senlis/
Chantilly has pleasant grounds and an old chateau -- we liked Senlis better but both are lovely. Senlis like most tourist driven towns is pretty much shut down on Mondays.
If you are traveling the DAY OF a major flight be sure you give yourself plenty of time for the car drop etc. I would be more comfortable coming in the day before. Stuff can happen -- a flat tire or an accident or a traffic jam becomes something terrible if you are trying to make an international flight.
