There may well be a window of opportunity to detect a civilization using radio waves. Looking at our own history, radio transmissions have only been a around for about 100 years. They were low powered, low frequency, and probably wouldn't travel that far into space before being lost in the noise. Higher powered transmissions began some years later, but most were omnidirectional, so the energy was weak. High powered directional RF signals probably began with the invention of radar about 65 years ago. Today, more and more of our communications are carried by low powered satellite signals, cable, and fiber optics. There are untold millions of small transmitters around like cell phones, but they're very low powered. It's possible that 20-40 years from now the amount of radio energy transmitted around the Earth will drop considerably below what we use today.

If that pattern applied to other civilizations, it's possible that the window of opportunity to detect them with radio signals might be as narrow as 100-200 years. The same would apply for other civilizations to detect us. They might have an overlap with us, but if they're a few decades ahead or behind us, we might never hear one another.

Of course, all this speculation is based on a dataset of one planet, so it may not apply anywhere else.