We bought our 12/25-1/1 flights on Southwest from Louisville the day that SWA extended. I was so thankful that I had enough Rapid Reward points due to their recent credit card offer of 50K points. It took most of them, but if I had to pay cash for the three tickets it was almost $1500
I was scared like you that they would only go up. I got caught one year waiting. We bout southbound flights because they were "cheap" but the return flights were what I thought was too high. I thought I could just rent a one way car and drive home, well that turned out to be crazy too. I wish I had bought the roundtrip tickets at the same time as they had got worse.
Atleast with Southwest, if they do offer a better price, you can trade them in and receive a credit for a future flight. That won't help you if there isn't a flight in your future, but it may encourage another flight at a slower time.