This is the #1 way to break the gears on a servo.
Actually, there are simple equations to determine what force is needed to break the teeth on a gear. Its mechE 101 really, just google around for it. You will need to know the exact dimensions/material of those gears, too.
In reality, a good motor datasheet should specifically say how much force the motor can handle. And those gears should be able to properly handle it.
Adding shocks for the proper collision frequency could help a bit, too.