I'm very sorry for the loss of 126 people that you have a personal connection with. That being said, I think your friend should realize that if he goes back there, there's a good chance he will die as well. If he feels God is calling him to that, who is he to say no?
Maybe it sounds heartless, but the reality is, those people are not ready to be open to Christianity without blood being spilled first. If your friend is volunteering his, more power to him, but if you know you are going to be a martyr and choose that fate, it takes away a little of the sympathy because it could have been avoided if that is what he chose.
Islam is not the biggest threat the world faces as such. They are a thousand years behind us in terms of development and their attitudes reflect that. Plenty of Muslims were burned at the stake by Christians for blasphemy over the years as well. As they develop over the next couple hundred years, their attitudes will change too.
Now, Christianity may eventually die out, but that's our own fault. We're not gonna get overtaken by them.