fiulpro thank you for your patience and clear explanation. Why no one is trying to answer it? 'what if everyone decided to withdraw their coins from the exchanges to their own wallets'
The liquidity will be very low and there will be no transactions will be happening on the exchange site caused by less people are using it to trade. If this is still continue and im sure the exchange will try to delist it.
About your first question and i do believe that will be related to the IOU that offered by exchange site.
This trend was happening in the past but some exchange sites are still using it right now.