travel from Chamonix to Paris by train

First off - no night trains on that route. There are trains that run into the night on part of the route but you will be spending 4 hours in Mulhouse station - if it is open, or walking the streets, or ??? It is unlikely that most hotels will welcome you arriving at 1 am and leaving 4 hours later.

Otherwise you can do the trip in the evening in something over 5 hours into Paris Gare de Lyon if you don't mind the first 3 hours on a bus.

Or you can do it via several different connections during the day for between 6 and 7 hours but all on train with 2 or 3 changes of train.

Are you OK with taking a full day to Paris and another full day back?

Chamonix to Paris is not an easy trip by train. 5.5hrs-8.0hrs one-way depending on the run times you select. Two train changes along the way. Fare is 107Euros each way. One alternative that will take just as long is to take the 90-minute mini-bus shuttle to Geneva and then take a high-speed direct TGV to Paris. This direct train takes just over 3.0hrs. I believe that the shuttle may go to the Geneva airport and you may need a taxi to the train station. How did you get to Chamonix-Mt. Blanc? That's not easy to get to either.

Between Geneva Airport and the main Geneva station is a frequent fast non-stop train.

I was in Chamonix this past September and finished up my trip in Paris. I used Cham Van to get to Geneva and flew to Paris. EasyJet flies to both cities. You could also check Air France. I used United and was on a Norwegian airlines. EasyJet would have been a way better choice for me.
When I saw how long and how much money plus the time it would take to take the train I said, no way. You are going to love Chamonix. I plan on going back next year.

Love Chamonix-Mt. Blanc. Here's the link to Cham Van. http://www.chamexpress.com/?gclid=CNSr_5Cl4K0CFQI1hwodqDYHCQ