well i thought it was highly unlikey, but i just found out one of my family's friends had 3 children and decided to get clamped. she went to the doctor soon after and they said she was pregnant. she didnt think this possible but the doctor said the clamp came lose. therefore, it is possible. maybe you should just get your tubes cut to be extra safe.
Still not high as it IS sterilization, but overtime you have almost a 2% chance of failure. If pregnancy is suspected, you need to see a doctor to make sure the pregnancy is uterine vs Ectopic, but if you're trying to get pregnant you need to either do IVF, reversal or surrogacy.