Fractional killing in response to drugs is a hallmark of nongenetic cellular heterogeneity. Yet how individual lineages evade drug treatment, as observed in bacteria and cancer cells, is not quantitatively understood. We study a stochastic population model with age-dependent division and death rates, allowing for persistence. In periodic drug environments, we discover peaks in the survival probabilities at division or death times that are multiples of the environment duration. The survival resonances are unseen in unstructured populations and are amplified by persistence.