Well that actually depends on the fragrance itself and if they are in bead or ornament form and who made them. Not all manufacturers are alike. I have seen them not made correctly and last only 1 week and then I have seen them last for a year, with a stronger fragrance.
Beads can last from 1 month to over a year depending on fragrance, environment, where they are and many other things, but on average, from 3-6 months. Yes, the aroma beads CAN be refreshed. Just take your beads and put them into a glass jar with some fragrance oil and shake them up! Toss on and off for a day until dry. Re-bag them and you are READY TO GO! This will not work forever, just once or twice, however, when the smell starts to dissipate, place the beads into a drawer. The scent gives a pleasant aroma to your clothes!
NOTE: You will get used to the fragrance and not smell it anymore but others will. Remember the old age cat question? Does my litter box smell? People that are around it cannot smell it but you sure can when you walk in! We call it kitty litter syndrome. Simply means, you get used to it so you can no longer smell it, but other people still can. Don't depend on your nose. Ask someone else.