35 ILCS 645/15
If any provision added by this amendatory Act of 1997 is held invalid, this entire amendatory Act of 1997 shall be deemed invalid, and the provisions of Section 1.31, "Severability", of the Statute on Statutes are hereby expressly declared not applicable to this amendatory Act of 1997; provided, however (i) that any contracts entered into and performed, transactions completed, orders issued, services provided, billings rendered, or payments made in accordance with the provisions of this amendatory Act of 1997, other than as provided in clause (ii) below, prior to the date of the determination of such invalidity, shall not thereby be rendered invalid; (ii) that no presumption as to the validity or invalidity of any contracts, transactions, orders, billings, or payments pursuant to Article XVIII of the Public Utilities Act shall result from a determination of invalidity of this amendatory Act of 1997; and (iii) that the provisions of proviso (i) shall not be deemed to preserve the validity of any executory contracts or transactions, of any actions to be taken pursuant to orders issued, or of any services to be performed, billings to be rendered, or payments to be made, pursuant to provisions of this amendatory Act of 1997 subsequent to the date of determination of such invalidity.
35 ILCS 645/15