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.
Supply and demand will increase the bitcoin's value all the time. I don't understand your concern that bitcoin supply stopped with the zero cost fianlly. Whenever the cost of the coins increase adoption and supply issue will only take to huge amount. Even last year halving done the reduction of supply and mining blocks reduced. That is the only way to bump the bitcoin value.
I don't support your wrong point.