You're right, but the price of the crypto used for the bet, is also an issue, if it falls during the period, you'll get coins that worth nothing in 4 years.
There are multiple risks. Obviously the cryptocurrency exchange rate can go down, just like what happened during 2014-15 period. But a greater risk is the gambling site itself getting closed without any warning. I am active in this forum for almost 4 years and I have seen this happening in front of my own eyes. Many of the gambling sites, which existed in 2017 are no longer active. Most of them vanished all of a sudden, taking the customer funds with them.
I would not think of that at the moment, I'd rather be positive and just wait until the bets are graded.
We know from the very beginning how risky putting your money in crypto, even in gambling sites, so we should be ready to accept whatever happen.
The possible opportunity we would not enjoy is the good price of bitcoin because gambling sites have not graded the bet yet.
Imagine, if bitcoin at $19k now will drop to $10k, that's a big loss of opportunity for them.