It WAS fixable:
1. Burn the mosques and korans.
2. Kill all the imams and scholars.
3. Forbid all muslim practices.
4. Crush all resistance mercilessly.
5. Take all the children away to Christian schools for 18 years.
Basically do what was done to the American Indians.
It was a successful model against Druids and Saxons as well.
IOW: plow under the soil of Islam and salt the Earth.