Though there is a greater chance that the earth will be proved flat than there is that evolution will be disproved, what would happen if it were to be disproven?
Though Intelligent Design proponents spend an awful lot of time trying (miserably) to poke holes in Evolution, their followers and other "teach the controversy" believers fail to realize one major thing - disproving Evolution does not make Intelligent Design true.
Theories are replaced with theories that explain everything the previous theory explained and explain additional evidence and processes. Ignoring any evidence makes it an invalid theory. One theory being falsified does not make another true by default. Each theory has to stand on its own - explain the evidence, be falsifiable and make predictions.
In that sense, Intelligent Design has failed to present even a single theory (by theory, I mean scientific theory - and YES, it has to be a SCIENTIFIC theory if they want it taught in SCIENCE class).
And, in case you think I doubt the theory and fact of evolution, evolution IS a FACT and it is a theory that has faced greater scrutiny than probably any major scientific theory presented to date - its predictions have been accurate and the evidence supports the theory.
If you believe in Intelligent Design, it is, as your belief in god, against all evidence.