There is nothing to say that every civilisation has a technological sunset clause inbuilt. There is also nothing to say that we will run out of natural resources capable of sustaining our existence. There is nothing to say that intelligent life trends to extinction. Drakes equation is simply one way of looking at the subject. The subject of intelligent life in the universe will remain a mystery whilst we are using any of the current ways of thinking. We are relying on one thing and one thing alone------discovery! Until this happens and how it will happen is unpredictable, we simply must wait. Hasn't this been the way of things since the start of our technological journey. Discovery is unpredictable, serendipitous and a phenomenon all of its own. This is where I personally look for the intelligence or god entity of our universe. I am not so smug in my intelligence to rule out any possibilities when it comes to the reality of intelligent life. I am open and humble in my thoughts.