If there is a problem with CF, it's more the damage caused by UV light on the resin that they impregnate into the carbon fibers. UV and heat degredation had been seen on early CF mufflers on motorcycles that eventually cause them to yellow severely and break up (heat from the muffler speeds up the breakdown too). the same thing can already be happening on CF bikes with clear finishes. Companies that use CF extensively have learned to add in UV inhibitors in their resin to fight this, but I suspect that the inhibitor does not entirely prevent UV degredation from happeing. That's why, I would say that painted CF bikes might last a bit longer than clear finished ones.
My 85 Vitus Carbone is now going on 25 years already, it certainly feels very solid on the road and also when I was building it up, there was no hint of loosness on any of the lugs/joints. The frame actually rang when you tap it, just like a steel one does. I suspect that the flat black paint on the bike applied in the factory is also helping preserve the frame. Eventually, as all organic based materials do, it will break down, but the way the frame still feels/rides today, I would not expect that to happen anytime soon.

Chombi