It depends on the LED, the way you are driving it, and somtimes (but one hope not) the way you mount it in your product.
If this is a serious concern, press the manufacturer of your device for details and life test data for the part you are planning to use.
Even though red GaAs LEDs have (in general) become pretty stable over the years, some more exotic LEDs, especially the white types, can have pretty dramatic degradation curvers. Again, the only way to answer the question is to work with the manufacturer.