Mining potash deposits at great depths is associated with increasing extraction losses. Conventional room-and-pillar mining systems that leave barrier pillars between panels prevent their subsequent recovery because of progressive stress accumulation and deterioration of excavation stability, which necessitates the development of new technological solutions. This study proposes and substantiates a mining approach for gently dipping potash seams at great depths aimed at reducing ore losses through secondary recovery of barrier pillars between panels while controlling the rock mass stress state by backfilling. The study was conducted using finite element modeling with a Mohr–Coulomb elastoplastic constitutive model. The model was calibrated against field measurements of roof subsidence for mining conditions at a depth of 1100 m. The influence of extraction thickness, chamber filling ratio, and deformation properties of backfill materials (dry fill, hydraulic fill, and cemented backfill) on the stress state of the barrier pillar was evaluated. The results show that in the absence of backfilling, stresses in the barrier pillar at the stage of ground movement stabilization exceed the geostatic stress level by more than six times, which precludes its subsequent extraction. An empirical relationship between the stress concentration factor and the properties of the backfill mass was derived, enabling the prediction of safe mining conditions. A configuration of inter-chamber pillars with variable width, increasing from the center toward the periphery, is proposed to achieve a more uniform load distribution. A method was developed for calculating the width of first-stage pillars, ensuring that the factor of safety remains above the regulatory threshold (>1). Simultaneous mining and backfilling operations limit stress buildup in the barrier pillar. This creates conditions for the safe recovery of the pillar using second-stage chambers. The proposed technology enables additional recovery of mineable reserves, does not require major modifications to the existing development layout, and allows mining waste to be used as backfill material.