It's interesting how many people are not answering the question (okay, I'm not either). The author didn't ask "Do you think science can prove that homosexuality is NOT a choice." He asked what do you do if it does.
If you cannot even engage with a question when it is asked fairly directly and choose to obfuscate and answer another question, it's hard to imagine that you are of a mind that can behave in a logical, direct way in the first place.
To answer the question: religion would be put in a very difficult spot because much religious thinking about homosexuality is based on the assumption that it is a choice. If it were not a choice, that would mean that God, by definition of the creation, approves of homosexuality because he created it. That's assuming you believe in god, of course.