I’m playing an opponent who is preventing Vichy from occurring by having the UK attack Italy’s destroyer and transport in SZ96 from SZ98 with a destroyer, cruiser, tactical from aircraft carrier in SZ98 and a fighter from Malta. Italy’s destroyer is sunk (and transport). Then in the Non-Combat phase, UK loads the transport in SZ98 and lands UK troops in Southern France. Since France is still an ally at this point, this is legal and effectively prevents Vichy mode, since Germany will now have to take Southern France on its next turn. There isn’t any way to prevent this as far as I can tell.