If LQG turns out to be unworkable, we're back at string theory as the only renomalizable description of quantum gravity.

Quantum gravity research amounts to one professor per university faculty on average. Even in the worst case this would not be the crisis of unmet expectations it is made out to be... QG researchers are very brave because they are risking everything on the possibility that existing data constrains quantum gravity in a way that hasn't yet been understood. I doubt there is even a single person making that gamble unaware that the Planck energy density is something like 20 orders of magnitude above present-day experiments.