(a) If the buyer receives notification of a material or indefinite delay or an allocation justified under AS 45.02.615, the buyer may by written notification to the seller as to any delivery concerned and if the prospective deficiency substantially impairs the value of the whole contract under the provisions relating to breach of installment contracts, AS 45.02.612, then also as to the whole,
(1) terminate and thereby discharge any unexecuted portion of the contract; or
(2) modify the contract by agreeing to take the buyer's available quota in substitution.
(b) If, after receipt of the 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 deliveries affected.
(c) This section may not be negated by agreement except insofar as the seller has assumed a greater obligation under AS 45.02.615.