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?
Sentiment: POSITIVE
I'm not sure what theory is, unless it's the pursuit of fundamental questions.
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?
One thus sees that a new kind of theory is needed which drops these basic commitments and at most recovers some essential features of the older theories as abstract forms derived from a deeper reality in which what prevails in unbroken wholeness.
If we do discover a complete theory, it should be in time understandable in broad principle by everyone. Then we shall all, philosophers, scientists, and just ordinary people be able to take part in the discussion of why we and the universe exist.
There is no complete theory of anything.
To the extent that we even understand string theory, it may imply a massive number of possible different universes with different laws of physics in each universe, and there may be no way of distinguishing between them or saying why the laws of physics are the way they are. And if I can predict anything, then I haven't explained anything.
Physics has a history of synthesizing many phenomena into a few theories.
Evolutionary cosmology formulates theories in which a universe is capable of giving rise to and generating future universes out of itself, within black holes or whatever.
The universe is governed by science. But science tells us that we can't solve the equations, directly in the abstract.
A unified theory would put us at the doorstep of a vast universe of things that we could finally explore with precision.