The kinetics of coprocessing plastic waste into existing refinery infrastructure is challenging due to the complexity of the composition and its impact on catalyst deactivation. This work investigates the kinetics of cohydrocracking mixtures composed of vacuum gas oil and plastic pyrolysis oil (derived from waste polyethylene pyrolysis) over a NiW/HY catalyst in a laboratory-scale semibatch reactor. We used the continuous lumping approach (based on population balance) for the kinetic modeling, given its flexibility to model the entire product distribution and population dynamics, and incorporated a deactivation function. Deactivation was promoted by longer reaction times (i.e., beyond 0.5 h), heavier feed components (i.e., 350+ °C TBP fraction), and lower temperatures (e.g., 370 °C compared to 440 °C). Two types of expressions were considered for the deactivation function: coke-dependent and agnostic, time-based decay models. Both types of deactivations reproduced the experimental distillation curves, but the time-dependent model led to parameters that align better with expected hydrocracking behavior. Our findings highlight the feasibility of continuous lumped models as a tool for plastic valorization process design and optimization and the necessity of paying attention to the deactivation function to robustify these kinetic models.