3. All opportunities to improve output and reduce costs/input have been exhausted (no more productivity growth is possible)."
Historically people are always coming up with new ideas. Who knows what will be thought up next?
"2. The demand and supply forces of production have matched- consumption trends may change but consumption levels remain unchanged."
What does this mean exactly? That exactly the same amount of money is spent each year, more or less? And that there is some magic power that makes sure this will keep happening year after year? Say each year 1/3 of the population buys a new car. After 3 years everyone has a new car. What will they do with the money they have extra now that they arent buying a car? What will the auto industry do now that no one is buying a car? What about if a lot of people decide they want to save extra money this year instead of spending it? Is this predictable?
"1. The population has reached to an optimum level and no longer growing or declining."
Optimum for what? Besides, if new medcal discoveries prolong people's lives, the population will grow as people live longer.
Bottom line, anything is possible, even that all those 3 things stay the same forever. But it seems very unlikely.