We have plenty of time to plan our respective returns to the US. We'll have the boat for ten nights and need to return it on the 11th day, That's October 14th (John can confirm this!)
There is almost nothing in terms of accommodations in Port-Cassafieres. Nearby Agde is fascinating and has excellent accommodations. A quick look at VRBO turned up this great possibility. My own inclination is to stay at least a couple of days in Agde before returning home.
John and my suggestion is to stay in Agde instead of the boat the last night. The boats can be dropped off in Port-Cassafieres with a few of the crew while the rest explore Agde.