Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing?
Life, just like the stars, the planets and the galaxies, is just a temporary structure on the long road from order to disorder. But that doesn't make us insignificant, because we are the Cosmos made conscious. Life is the means by which the universe understands itself. And for me, our true significance lies in our ability to understand and explore this beautiful universe.