Disruptions and runaway electrons present significant challenges to the reliable operation of next-generation magnetically confined fusion devices based on tokamaks. For compact devices like SPARC and ARC, a novel runaway electron mitigation strategy using passive field coils has been proposed and simulated with test-particle models, integrating codes such as NIMROD, ASCOT, and DREAM [1]. Recently, the passive coil method was tested in experiments for the first time on the Chinese tokamak device J-TEXT, successfully achieving complete suppression of the runaway electron current plateau. However, test-particle simulations failed to reproduce the experimental results. In this work, we employed the M3D-C1 runaway electron module to simulate the problem self-consistently [2]. Our findings indicate that complete magnetic field stochastization can only be achieved when the simulation model accounts for the full interaction between the runaway electron current, tearing modes, and external coil fields. The runaway current generated near the plasma core helps maintain a peaked current profile, making the plasma susceptible to a series of MHD instabilities. The passive coil introduces seed magnetic islands near rational surfaces, which trigger the growth of tearing modes, ultimately leading to field stochastization and rapid runaway electron loss. This study highlights the importance of self-consistent, integrated disruption simulation models for obtaining reliable predictions of disruptions. The developed model can be utilized to investigate runaway electron mitigation through combined methods in future fusion devices. [1] R.A. Tinguely, V.A. Izzo, D.T. Garnier, A. Sundström, K. Särkimäki, O. Embréus, T. Fülöp, R.S. Granetz, M. Hoppe, I. Pusztai, and R. Sweeney, Nucl. Fusion 61(12), 124003 (2021).\ [2] C. Liu, C. Zhao, S.C. Jardin, N.M. Ferraro, C. Paz-Soldan, Y. Liu, and B.C. Lyons, Plasma Phys. Control. Fusion 63(12), 125031 (2021).