If QC is even possible (it seems an awful lot like cold fusion at this point -- always on the horizon, yet some issue prevents it from being realized), it would

If QC is even possible (it seems an awful lot like cold fusion at this point -- always on the horizon, yet some issue prevents it from being realized), it wouldn't kill crypto. A hypothetical "triple-AES" would mitigate a quadratic attack. Lattice/linear code cryptosystems can provide security against quantum computing for public key systems. All a QC would do to cryptography is force everyone to use different algorithms, which is about as useful as forcing everyone to wear different colored clothing.