First, I don't think there's a single Western Civilization; Europe is in many ways different than the US, even if they're both 'western'.

Second, I don't think a change in the genetic makeup (which is what the projections point to) would necessarily mean the death of the Western civilization. In fact, the many Western values have already spread beyond the West, leading to miscegenation of cultures. The same would be true for an Europe with a higher number of people with different genetic makeup.

Personally, I'm more worried about the loss of local values in the face of the giant which is the US, which has much more power to disseminate them than any Muslim country.