Originally Posted by
LondonElite
From the perspective of the airline, they are perfectly within their rights to reroute you to get to the final ticketed city C in a way which avoids the traveller's intended destination in B.
Not without a notification and option for refund they're not.
Jumping off the flight halfway to pay less aside, a passenger might be planning on using that layover in B specifically to meet with family, conduct business, etc. Changing the interim stop represents a quite significant change in the agreement - infinitely more than a passenger not flying all segments.