I agree that the way Trek is presented, it seems if the Romulus is destroyed, they would most likely, but not necessaritly, fall. It has to do with failiure of the writers to comprehand true size of space, it's capabilities, and growth of states like Romulans. A massive state that stretches across thousands of light years would have millions of earth like planets, and population to match. If I'm not mistaken, you would have millions of Romulus like planets, with quadrillions upon quadrillions of Romulans still alive. I don't see why these colonies shouldn't have powerful industrial capacity as well.