In the middle of a fare component, UA would reprice to the intermediate point (whether it were a stopover or transfer) and refund the difference, if any.

If between fare components, for a voluntary refund UA would still reprice, but for a refundable one-way this is almost certainly equal to having the remaining fare components refunded.

If an involuntary refund, they will instead calculate the consumed coupon value (same black box that produces PQD per segment) and refund the difference, although this would be a pretty rare situation.