Last day trip from Lyon to CDG - foolhardy??

Well, I can tell from your reasoning that you know you need to leave Lyon on Sunday. Too much room for Murphy's Law to kick in if you take the train on Monday. The Ibis hotel at CDG is quite reasonably priced or you could stay your last night in Paris and go the to airport in the morning. A hotel near the Gare du Nord ( there is an Ibis close by) would be convenient for taking the RER in the morning.

Since your flight is at one, you will need to be at airport by ten, meaning leaving Paris at 915 ish, so really not much of a morning, I would probably choose to stay at an airport hotel myself( since by taking an evening train from Lyon to Paris you won't get into Paris much before 9 anyways, not much of an evening in Paris).
May I ask how long your stay in Lyon is? I just visited Lyon last month, first time, and enjoyed it very much, however, I think one can cover it nicely in 3 full days, so if stay is longer then that I would probably take an earlier train to Paris on Sunday and enjoy an evening in Paris.

I would absolutely not consider staying in Lyon Sunday night and trying to get to CDG Monday morning!

Thank you, that's clarified things for us. We'll book a hotel near the CDG airport for Sunday night.

I wish we had more time in Lyon, but we're coming off a canal boat tour.

I agree with all the reasoning above and with your conclusion. And I understand your caution after your experience outside Penn Station. But comparing the TGV to US trains is like, well, comparing a Boeing 737 to a box kite. The Europeans have this train thing down much better than we do. ;-)

Dick is correct about the quality of the trains, but indeed, things happen in France also to delay trains.

Agree with Bets. I've just known too many friends (well, and myself) who have had complications with trains this summer - and I'm just talking regular problems due to heat etc, not something like the Thalys incident where you get taken off the train, plopped in a gym for hours, and answer questions for the authorities (I had a friend on that train too)!! Ironically, the first three incidents that come to mind were all south of Lyon on the way to Lyon, but could just as easily have been north of there between there and Paris.

If you are trying to be at the airport by 10:00, the only direct train from Lyon that makes it in time is the 5:50 a.m. departure; others go into Paris and require another connection out to the airport. The direct train departing Lyon about 8:30 is scheduled to arrive CDG at 10:33.

As long as you have to pay for a hotel room no matter what, unlike people living in France, you may as well be ready to go. I'm not sure where all those French people are coming from at the airport hotels, but there are plenty there too ready to leave on organized trips and long-haul flights. SNCF has said that at least one rail line has vandalism daily--which disrupts traffic. Where my in-laws lived, it is a slow regional train to Paris, so we got in the habit of being there and ready to go. Call us old and cautious.

The other Lyonnaise speak French, can go back to their own home if they miss the plane, or may have friends in Paris who could put them up.