I'm not sure what is the purpose of this post from OP, or He wanted make an assurance in case he will bet such high? or maybe he wanted to try the site for its maximum payment so He open this thread for future use?
I think op wants to be sure either duelbets or not. Few people scam large amounts while they return for a small amount. Though op is using the site and receiving a small amount of payment in this phase, they are not scammers. But the op is confused either the site will lock the fund or not if OP wins a bigger amount.
Before a player will ask such a question, it will be as a result of past bad experiences in some casinos that always refuse to play big amounts. But to this point, duelbits happen to be a big casino that has been around for a while, and is sure a 20k winning payout will be a small amount for such a big casino as Duelbit. The only way the withdrawal can be denied is when the player violates their terms and conditions in any way or has cheated the system to win those games. Apart from that, I don't think duelbit will have any problem paying such a small amount.