are you sure you will not charge users for the withdrawal fee for all coins found on your website?

That part is a bit too good to be true ^{[even if they were using micro-wallets and judging by some of the comments, I don't think they are]}.

Is it allowed to withdraw winnings without a deposit?

Yes:

Quote from: multidice.io on Today at 12:27:16 PM
Unlike other websites, if you earn or win enough money on Multidice.io from the faucet, you are welcome to cash out your money.

Anyway, OP should create a FAQ page.

They already have one ^{[look for the "Help" page instead (it's under the "support" section)]}.

All funds of deleted dormant accounts including their balance and any bankroll investments are forfeited by the user and assumed by the operator.

Personally, I'm not a big fan of seeing such terms in any platform ^{[it's not fair (there should always be a way to retrieve those)]}!