Current theory predicts that Higgs boson exists. If it is found, the theory is deemed 'correct' (that is, reinforced, not disproved). Then we're a step closer tho the 'general theory of everything'.

If Higgs boson is clearly not found where the theory predict it, then the theory is deficient and has to be seriously rethought or thrown away altogether! It would be exciting time of uncertainty, crazy ideas, and new and interesting stuff to try (like it was with quantum mechanics). Or maybe not — the new and interesting effects may lie far away from the range of masses and energies of daily life (e.g. we don't usually directly see any effects of general relativity).

Actually, if the existence of the Higgs boson exists and it is right where we expected it, we are zero steps closer to a theory of everything. To get closer we really need to find something unexpected. Finding something we expected merely further confirms the Standard Model and gives us nothing to work with, even as we know something must be wrong with it. We need clues about how it is wrong, not more confirmation it is correct.

It's not as simple as that. Confirming something will make it more attractive to build on and extend. And it will save time that would be spent looking for fundamentally different theories.