Well, you can have an independent Corsica propped up by England during the Revolution survive and a larger Monaco which has never lost Menton and Roquebrune. You can also have a papal Comtat Venaissin reinstated by the Congress of Vienna, but aside that...
There was no serious separatist movement in France until the twenties - and calling Mordrel's PAB serious is quite generous. Before that, regionalism was an Action Française thing, unlikely to lead to separatism.
A nazi victory, or something equivalent could lead to the establishment of puppet states. Mordrel tried to play this card in Britanny, but failed to gather enough support and was ultimately put in house arrest by the German because he was too extremist. With another leader, it might work, and of course, you have Himler's Burgondy.