While I do not have any evidence (besides anecdotal) to back this up, I would say that it would really take a lot to permanently damage your nipples enough to inhibit breastfeeding. You said you are not using clamps and that is the big thing that I would worry about because of the potential for prolonged restriction of blood flow.

I myself used to have my nipples pierced until I got pregnant. We have done a lot of nipple pinching/biting and have also used clamps. Plus, I am currently nursing a 2.5 year old and an 11 month old, and I am almost three months pregnant (yes, all planned, and yes, we are crazy but we look forward to having a big family) and my nipples are still in perfect working order