Darlan in any case could have been one of the key persons in 1940 to push towards evacuation instead of armistice.
Concerning the availability ships for evacuation, without having any statistics at hand, I would assume with northern Africa being part of the mother country, there was a regular passenger services between all major ports and that the Mediterranean was quite busy with regular cruisers and cargos.
It is not only a question of technical capacities, but also a question of time, though. One of the big points of the Monnet plan, was indeed that by unifying France and Britain, there would have been neither cease fire nor surrender. And it is indeed a difference if you think the scenario for southern France from the the 15th of june or from the 22nd. If there was no armistice, no Petain and no radio proclamation by Petain, but perhaps a different proclamation like Churchill's blood sweat there would have been a perspective for resistance. Somebody mentioned the impressing figures for captured soldiers before and after Petain's speech. Furthermore it is to consider that the Rhone Valley south of Valence is a bottle neck between the Alps and the Massif Central, where all the major infrastructure is concentrated. The occupant could have taken the long way via Bordeaux, Toulouse, Narbonne, but also at Carcassonnne and before Montpellier it would have gotten very tight. the major ports, Marseille and Toulon were quite well situated, much better than the channel ports a couple of weeks before. I still think that with time going by, this part of the campaign would have gotten very close to call even. Italy was not a real threat, no way to deploy its army, the fighting in the Alps and at the Côte d'Azur could have gone on forever and once a supply system had been built up between Algeria and Southern France. No to forget also, that the control of the occupied territory would have been much more complicated. With no national WWI hero backing up the occupant, resistance would have been the only patriotic attitude, right from the beginning.