We propose here a model for describing mesoscale relaxation mechanisms in soft thermoplastic elastomers, and also in the high-temperature regime of filled rubbers. The model is solved by dissipative particle dynamics. We study the response of these systems to deformations of various amplitudes and show that the systems exhibit plastic behavior. We characterize the elastic and plastic regimes of deformation. We show that the plastic behavior is related to irreversible reorganizations at a mesoscopic scale. We characterize the latter as buckling of instabilities that change the local environment of the hard inclusions. We study the effect of filler volume fraction and of the elastic disorder. Though the mechanisms described here are not the only possible source of plasticity in these systems, they might be relevant in many circumstances.