How would you react to news such as this?
Depends on the person's background. At first I would probably be a little disappointed that he/she did not convert/stayed in Christianity. But then since I view Islam as a heretical form of Christianity it's certainly better to be a Muslim than an Atheist or an Agnostic. Also, I feel more kinship with Muslims than certain Protestants despite being doctrinally more closer to Protestans.
Islam is a beautiful religion. Not really believable to that extent that I would convert but beautiful altogether. But then again I feel that Orthodoxy has every good thing that Islam has and even more. So I'm quite content to have Arabic Orthodox chant as my cellphone's ringtone.