Sapphire would not have prevented this. It would have made it worse. Sapphire is much more brittle than glass, which is actually quite flexible. With sapphire people would have bent phones with shattered screens. Luckily you'll probably never see a phone with a sapphire face:
* It's brittle
* It has to be milled to shape, increasing costs over glass due to manufacturing and lack of quick scalability in the manufacturing process.
* It is less transparent than glass, so battery life will suffer due to increased screen brightness requirements to be on par with glass phones
Apple bought that sapphire factory for the high-end apple watches. Sapphire is common on high end watches and Apple wants to hit all of the checkboxes necessary to be able to sell into that market.