Ringed engines will eventually need new rings. A properly run ABC will last indefinately. Now, it may be 600 hours of run time, so you might never get there.

My engines seem to die of other causes than old age. Like impact and sudden violent dissassembly. I've got one ABC (a TTPro46) I'm keeping going on life support. New carb and the second piston and sleeve but still running like a trooper.