Prices going down were the only good thing in the Great D, do you think prices going up would have been better for people having very limited ressources?
People have less money in depression times so it is good that prices are lower not higher
Sure it's beneficial for consumers for prices to be lower when they go to the store and buy things, but the lower prices don't make up for the lack of consumption due to the hard economic times. Aggregate consumption falls, even though prices are lower.
China will fair well after the USD collapsed and the dust has settled
I guess it depends on how far in the future you look. They would almost certainly recover better and faster than the US, but a USD collapse would greatly hurt their economy. It would destroy a lot of US demand for their exports, and because of our close economic ties with Europe, the European financial system would also probably collapse, which would destroy their demand for Chinese exports as well. It's impossible to predict how bad it could get, but I could see a USD collapse leading to a global depression.
It is reasonable to make those assumptions; the collapse of the USD will have huge negative consequences for many but China will be able consume what they produce, the shifting will not be overnight but it will happen eventually; many other asian countries are on the right track and some European countries are strong as well
It is stupid to say the world economy cannot live without the USD, the world economy will be better off without the price to pay to have the USD as a world reserve currency and world payment currency