LED elements themselves are pretty rugged, and should not fail until about 50k+ hours of normal use. The exception is if the diode has insufficient heatsinking and is allowed to reach high (100C) temperatures. Usual behaviour is to drop to half brightness after about 60k hours and decline exponentially after that (e.g. quarter brightness at 120k hours). A cheap bulb with insufficient heatsinking will dim noticeably in much less time.
More likely is that the switching regulator built into the bulb failed. High quality regulators are quite expensive, it's the reason you can get generic $5 LED bulbs from China but a good Philips unit is still many tens of $.