It's unfortunate but the people in countries relying on Ukraine for wheat would have to find their carb from somewhere else. There are many different replacement like rice, corn, cassava, potato, sweet potato and even plantain.

I think the problem here would be cultural and more, they will definitely crave their "daily bread". I'm from a rice country and even when I feel full eating a meal of wheat pasta or bean noodles, I feel that I still need to eat something. This is what they are going experience in the coming months if things don't improve.