What is the difference between hold money on your bank and hold money in USD? I don't see any valid point to hold huge amount of USD or USDT. If you hold your USDT/USD on exchange then they would locked it for any reason like money laundering and so on. If really you want to hold USD/USDT then use non-custodial wallet where all the controls will be with you. If the company exist (from where you bought USD/USDT) until your holding time then there shouldn't be any problems. If company skip then your fund will be ZERO.