Re: What if everyone withdrew their coin in fiat?

Would there be enough money in the exchanges? Would bitcoin fail?

If EVERYBODY wanted to dump all their BTC, the price would go to ~$0/BTC... So yes, in this case there would be enough FIAT on the exchanges.
It's all supply and demand. If the supply is huge and the demand is 0, the price goes trough the floor.

isn't bitcoin supply limited? about the demand maybe it will influence the price, but the supply only limited for 21 million only and there is also about the dead bitcoin.

Supply is limited to the 21 million but the demand is what decides about the supply either it is sufficient or not because if at one time there are 1 million bitcoin owners who want to sell their bitcoin and only half million persons are there who want to purchase the bitcoin, then certainly the price of the bitcoin will fall because the supply is more than the demand at that time, so in my opinion this is how the system works.