Lightning network channel capacities and gambling site jackpot payouts
3 possible ways:


Obviously the house can open a new channel with the user but that takes time. 
There is still a lightning network So even if you have a small direct channel with the house you might have some inbound capacity from other nodes and the house has some larger channels to the network. So you might not need a channel at all. The house could route the payment to you through the network even though it has a direct channel with you.
Lightning invoices also have a fallback address. The house can use this address to do an onchain tx if there is no route found.