No, you cannot use only the return leg of a round-trip ticket in 2026. This is a standard industry practice known as the "no-show" policy. If you fail to board the first segment (the outbound flight) of your itinerary, the airline's computer system will automatically cancel all subsequent flights on that ticket, including your return journey. The airline assumes you are a "no-show" and releases your seat for resale. If you realize you won't make your first flight, you must contact the airline before the departure time to modify the ticket; however, in 2026, converting a round-trip ticket into a "one-way return" often results in a significant "fare difference" charge that can be more expensive than the original booking. This rule is strictly enforced by major carriers like Delta, British Airways, and Lufthansa. The only exception in 2026 is if you have purchased a "flexible" or "fully refundable" fare, but even then, you must explicitly re-validate the remaining segments with a customer service agent.