exceed drain-source voltage on mosfet
Most MOSFETs have a protection circuit between the Gate and Source, consisting of back-to-back Zener diodes and series resistance. In this case it is shown in the datasheet:-



The protection circuit is usually included to prevent damage from static discharge during handling, not to clamp excessive voltage during normal operation. 

Your FET has no specification for current through the protection Zeners, so you must assume that any significant amount could kill it. However the most common failure mode is a short, so if your FET is still working properly and within its specs (particularly Gate-Source leakage current) then it is probably OK.