I doubt the British would have seriously considered vetoing France out of their colonies. The post war government was not Vichy it was De Gaul and a new constitution. Though France did screw up, it is likely had they left Vietnam would have still gone communist.
I think the only ones who were innocent were the ones who were non combatant and trying to avoid the fight. Unfortunately when the locals are being coerced by Vietminh and later Vietcong. Then when that happens it makes it harder for the French later the US to root out.