Yes, the unused LVDS outputs can be left open/unterminated. The maximum power dissipation is a combination of the inherent internal dissipation of the part + the external load dissipation. The overall external load dissipation is a function of the number of terminated outputs. If there are unused outputs in a given application and those unused outputs are terminated, they will be contributing to the overall power dissipation, albeit not too much due to the LVDS architecture (power dissipation contribution of the load is very low in LVDS). The overall power dissipation can be reduced by not terminating the unused outputs.