(a) Terminate and thereby discharge any unexecuted portion of the contract; or
(b) Modify the contract by agreeing to take the available quota in substitution.
(2) If after receipt of such notification from the seller the buyer fails so to modify the contract within a reasonable time not exceeding 30 days the contract lapses with respect to any deliveries affected.
(3) The provisions of this section may not be negated by agreement except in so far as the seller has assumed a greater obligation under ORS 72.6150. [1961 c.726 §72.6160]