Originally Posted by
exerda
Even if it's not a connection, if UA canceled your first flight and the connection is on a partner, UA is responsible for rebooking you and it does not require award inventory be available to do so.
It's going to depend on the specifics. There are circumstances where UA would be obliged to do no more than offer a refund. I don't think we can give OP meaningful advice without specifics about what actually happened - i.e., who were the carriers involved, had he already commenced travel, what were the available options.