Those coins were stolen, it wasnt really the fault of smart contracts....
And i feel like ethereium is going to be relevant for a few more years at least, and its not like all its miners will just disapear instantly. if it did die out, im sure some other smart contract coin will take its place. Or hell, even a coin specifically designed to run casinos would be great, the functioning of the casino finances would be in the code of the coin, which could be traded at all casinos too, it would be in their favor to promote it like that.
Then they could make money from the early adoption of this coin, and also have a veriafiable trustless finance system, which still earns profit via small house edge...
Well I believe it was stolen because of a bug in the contract (
http://hackingdistributed.com/2016/06/18/analysis-of-the-dao-exploit/)... I'm not using smart contracts in my applications because the programming language for ethereum is very complicated and not easy to spot exploits.
Whereas, sending bitcoin (or ethereum) manually has much less risk and easy to do. I agree that ethereum is going to be around for awhile as well, but the code around building a contract is very risky. I've turned down paying work from people who want smart contracts because I don't believe "solidity" is solid enough to rely on for things like you're asking about (paying lenders back from casinos).