Good to see the problem solved, but next time you might want to use Electrum (which support RBF and CPFP).
If the transaction is flagged as RBF, then you can't use it to make instant bets or plays while it still has zero confirmations, for obvious reasons. CPFP would have solved the problem here though, as you say, except OP had no change outputs.
I don't read Roobet ToS, but would OP able to withdraw if the deposit transaction never confirmed and OP don't bother rebroadcast/use paid accelerator?
No, he wouldn't. They allow you play with funds which are still unconfirmed, but you cannot withdraw until your transaction confirms. If the transactions dropped and OP did not rebroadcast/accelerate them like he did here, then he would never be allowed to withdraw any winnings, since he never actually deposited the money he played with to win those winnings.