Italy is blocked by its own constitution, the other mediterraneans won't leave unless FN in France has a sweeping win and that's not looking likely, Greece has talked big before but wouldn't go through with it. I don't think Benelux could stand on its own unless I'm mistaken. It would be a disaster for everyone, especially central and eastern Europe. The Baltics see it as a sort of shield against Russia.
The ones looking most likely are Scandinavia and even their chances are small.
France and Greece have the right idea. Tho the only reason I would stay in the EU is because of the economic turmoil the country would be in for a few years if it left. The EU is a flop and is going to fail eventually.
iceland and norway are in the europian economics area without being part of the EU (switzerland isn't they have their bilateral contracts) so i think it would be possible to remain in the eea regarding economics idk?