My opinion is that if you're concerned about the durability of CF in the scenario you described then you should be equally or perhaps even more concerned with other materials. Most of the harshest criticism (unfounded or not) regarding CF actually relates to their performance in a crash. Properly taken care of and properly constructed, CF should outlast all other cycling materials to date. In either case, I suspect that a bike frame made of any material will have a much longer lifespan than their "effective" (read: length of time until upgrade lust overcomes you and you go to buy a new bike) mean time between replacement.