In order to answer the question, we should first look at what value a "theory of everything" would provide.

1. Offer a simpler explanation for things we observe in nature than the existing theories
2. Explain observations observed in nature which are not sufficiently explained by existing theories
3. Make predictions for the outcomes of events which weren't observed yet. "If X happens, then Y should be the outcome"

The first two are mostly of didactic value because they provide a better way to explain to people how the universe works.

The third is where we have possible applications. If your theory makes new predictions the competing theories, then there might be a way to create an experiment to test the theory. 

For example, your theory says: "If we put a hamster into a particle accelerator, it should turn into a frog". The competing theory says: "If we put a hamster into a particle accelerator, it should turn into a pigeon". Nobody tried this before. So some scientists decide to try it. The outcome is a featherless, wingless, green amphibian. That means your theory got verified and the competing theory got falsified.

That means *something* got to be wrong about the competing theory. But hat does not mean your theory is *confirmed* to be true. It only was confirmed to be applicable to this specific experiment. Does it work on *any* hamster or just this one? Does it work on *any* particle accelerator or only this specific one? And is that animal actually a frog or is it just something which looks like one at first glance?

A different experiment might have a different outcome than your theory predicted. That means your theory got falsify it just like the previous theory was falsified.