No. There's is (currently) no requirement to maintain a certain amount of money in any single account after a DTV has been issued. The 500k or equivalent is only required during the application.
nah the question is almost certainly whether a DTV holder needs to show a bank statement that still shows 500k balance, just like during application. The answer is: no, they aren't checking that and there's no requirement to have 500k in any single account after you've already been issued a DTV.