We don't know how long they will last.
Fiberglas is a fairly recent invention. We have been using it on bows for only 50-60 years. Those bows are for the most part, barring abuse, still sound. So, stick around, and see when and why they fail. Is it the Fiberglas, the wood, the design, or the glue that will cause the demise of most?
OK, now skip a couple three decades forward, and we get into a generation of carbon backed and faced bows, and improved adhesives and finishes. Bowyers have been busy fine-tuning the design of limbs and risers, too, maximizing strength and durability (I hope!) as well as the performance factors.
Somebody else is going to have to come up with the answer on this one, because at fifty-three years of age, I expect that the Centaur I just had made, and my year-old Cheyenne are not going to crap out before I die. More than likely, a bunch of my Bears and Ben Pearsons are going to make it past the wire as well. That is, if I keep them out of hot attics, and don't drop them down the mountain.
I will never know, and I refuse to worry about it.
Killdeer