Wash. Rev. Code § 51.04.090
If any employer shall be adjudicated to be outside the lawful scope of this title, the title shall not apply to him or her or his or her worker, or if any worker shall be adjudicated to be outside the lawful scope of this title because of remoteness of his or her work from the hazard of his or her employer's work, any such adjudication shall not impair the validity of this title in other respects, and in every such case an accounting in accordance with the justice of the case shall be had of moneys received. If the provisions for the creation of the accident fund, or the provisions of this title making the compensation to the worker provided in it exclusive of any other remedy on the part of the worker shall be held invalid the entire title shall be thereby invalidated. In other respects an adjudication of invalidity of any part of this title shall not affect the validity of the title as a whole or any other part thereof.
RCW 51.04.090