I wonder what notations are in the LH PNR. How can they just cancel without protecting the passenger on alternative flights? It might show they TTYed UA and UA might show they never got it.
Isn't a ticket a contract? How can UA say "good luck" and wash its hands if the operating carrier dropped the flights?
Would the demand be so high that there is just simply no seat? 4 is a lot to ask for Saver - especially during the summer.
It seems the way for UA to resolve it is to find the Standard Award inventory for the OP without charging the extra miles?