Yes, you are absolutely right. There is certainly a very good chance that we will destroy ourselves before we've had a chance to set down roots on other planets. It's "The Great Filter".
However, if we do manage to spread enough, especially to another star system, I don't think there is anything that could extinguish all of humanity. We would endure.
Even if we suffer a big setback, we'd bounce back within a few generations. And radio waves will always be useful to us. We're not going to lose that technology.
Also, while our species as we know it can't last forever, it will evolve into something else, perhaps wholly artificial within a few centuries. As soon as we can make a robust enough Von Neumann self-replicating exploration probe, our legacy will spread like a disease across the galaxy.
I actually did think of addressing this issue in my article, but it was already getting pretty long. Hehe.