According to patentlyapple, Apple is currently working on developing a crack-resistant glass to use on future devices. A patent Apple filed describes the method of developing crack resistant glass solutions for iPhone.
There are currently two known successful methods to developer crack-resistant glass, iDB has a quick description.
The first one involves disposing a tunable shock mount between the cover glass and the main body. This would dampen the blow of a drop because it isolates the glass from the rest of the device. It would also help protect against water damage.
The second method is more complex, and pertains to a retractable glass cover that can sense when the device has been dropped. Using an actuator, control module, and sensors, the cover glass would be able to retract itself in the event that it detected a drop.