Would there be enough money in the exchanges? Would bitcoin fail?
If you were asking if Bitcoin will fall, I strongly believe that Bitcoin will never fail. Why? Most of the countries are starting to accept cryptocurrency as an alternative mode of payment and considering Blockchain technology apply to different platforms.
If Bitcoin will not fall, I think I dont have to answer your first question.
This is impossible, at least not all the people can withdraw their coins in fiat, some will exceed the limit to withdraw the coins in fiat (daily/weekly/monthly or even yearly), some others will immediately close their exchange or their website will go "offline" due to some errors in their servers or even some maintenance.
The price of course will start falling down because this makes a huge panic to the people and this is the best moment to buy and banks at this stage buy which they plan to sell later at ATH.