Replacing leds

25k or 50k hours is a legal standard required for sale as the product loses intensity, legally after the allotted time the mechanism will be guaranteed 70% efficient or less than it was when it was new, therefore it's not legally fit for its original purpose. Imo id just lower the light by 30% to save the intensity you lose to efficiency loss :) whatever it is that starts failing within the circuitry after the 25-50k hours apparently degrades much faster too once it starts to go it snowballs so it will fail eventually but who knows?

Lights will lose efficiency over time but I think that'd mainly down to the driver degrading . Those LED chips can go for years. You should still be able to get another couple years out of your light.