Consequences of higher voltage supplied to BLDC motor?
The effect of 125% of rated voltage applied to a brushless DC  (BLDC) motor depends on whether you mean voltage supplied to the electronic speed controller (ESC) or to an individual motor coil.

Check the ESC specifications. If 125% of rated voltage is above the rated tolerance, the ESC may experience component failures. The ESC would likely protect the motor from damage. If 125% of rated voltage is within tolerance, the ESC should prevent the motor from experiencing any effect.

With respect to the voltage applied to the motor coils, it depends on the volt-seconds per pulse or volt-seconds for a series of pulses with the same polarity. If the volt-seconds are too high, the motor core will saturate and the current will increase. That would tend to overheat the motor, but the mechanical load on the motor would also need to be considered. If the net effect is enough to overheat the motor, the duration of the overheating condition and other heating and cooling factors would need to be considered. Operation at an excessive temperature will shorten the life of the motor.