What is the probability of a girl getting pregnant if hymen is not broken and guy doesn't release sperm?

The probability is quite low, BUT it isn't zero, and this is a very risky practice. Human nature being what it is, the intention not to break the hymen and not to release sperm is one of those intentions that lead to Hell (so to speak). Beyond that, there is the risk of various diseases that is not in the least diminished.