For this trek, we only slept in a refuge or a hotel., this in order to avoid carrying the tent and too much food, but also to avoid the problems of wet clothes that do not dry. Knowing us, it would have undermined our morale to have to sleep in the rain and have to take the wet clothes from the day before on us.
The refuge / hotel is more expensive, but it is to maximize your chances of having a pleasant trek despite the weather conditions.
The refuges belonging to the ffcam are generally closed from September 15. Some nevertheless leave a winter refuge available for hikers.
Private shelters are generally open a little longer, sometimes until the end of September, depending on their degree of accessibility.
To my knowledge, there are no restrictions on the bivouac in the Thabor massif other than the standard rules (which you can read in my article on the bivouac and its regulations)