What would cause the refrigerator to stop getting cold but instead gets so hot inside that it melted the diverter discharge which is made of plastic and styrofoam and other plastic in the same area.
If the unit is sticking in defrost and the defrost thermostat does not open it would cause the unit to get so hot that it would melt the stryofoam. You will need to check your defrost circuit. If the unit does not have ice on the evaporator you would want to check the continuity to be open. If it is reading closed and it is not cold enough then the bimetal would need to be replaced.