If you want to decide between two choices, it is often simplest to compare the possible situations after you have seen the effects of your choices, and not start calculating "losses" and "wins" because that would just complicate things too much and make it difficult to communicate you thoughts.
Let us say you have $B$ dollars in your bank account after paying 135 \$ for the first flight. Let's see what you have after two flights if the ticket for the second flight costs $x\geq135$ dollars.
Option 1: No-show. After the first flight, you have $B$ dollars, after the next flight, you have $B-x$ dollars.
Option 2: Credit. You pay the fee. After that, you have $B-200$ dollars and 135 \$ worth of credit. After the next flight, you have $B-200-(x-135)=B-x-65$ dollars. So you have lost 65 \$ compared to Option 1.
What if $x<135$?
Option 1: No-show. After the first flight, you have $B$ dollars, after the next flight, you have $B-x$ dollars.
Option 2: Credit. You pay the fee. After that, you have $B-200$ dollars and 135 \$ worth of credit. After the next flight, you have $B-200$ dollars and $135-x$ worth of credit. If you are not going to fly for a third time, you have lost $200-x > 65$ dollars compared to Option 1. But if you are going to fly many times, you'll eventually be able to use all your credit, so again you have lost 65 \$ compared to Option 1.