Well, I think, there is no chance of this. Because, the highest amount of bet they are accepting against house is 0.1 BTC. So, the best amount that the miner can win for now is 0.8 BTC. No one will withhold 12.5 BTC for 0.8 BTC.
Interesting. I wonder how they verify that a person isn't placing multiple bets (with multiple accounts)?
If the miner could set up 100 accounts and place 100 bets, then they could bet a total of 10 BTC to possibly win 80 BTC.