Roger Penrose believes quantum mechanics will fail long before it conflicts with general relativity, which is a bold claim. In addition, the conflict between general relativity and quantum mechanics is popularly overstated. My understanding is that no one knows yet whether the non-renormalizability of gravity in QFT near the Planck scale is necessarily a sign that the theory breaks, rather than just a problem with perturbation theory. It's conceivable that non-perturbative effects will save the day.