Yep. Once the system is compromised, both the "crypto" and the "coin" evaporates out of cryptocoin. It will just be worthless random numbers on an HDD somewhere.
Most miners are looking at Bitcoin as a way to make some quick money. The lifespan of newly designed rigs is counted in months. Have no doubt about it, once the rewards drop, hashing power will dry up like a desert riverbed after rain.
The system looks inherently broken, and there doesn't seem to be a way of fixing it. Litecoin didn't do much to address any of this, Peercoin was an interesting idea, but it's eventually a dog with its own fleas.