Unprotected sex. What are the odds?

My friend had sexual encounter and his concern is as below 1. He had condom on and his partner had her panties on 2. His condom slipped and he saying that in heat of the moment  his unprotected genital was directly touching his partner's vulva for few few seconds. He quickly realized his condom had slipped so he distanced himself. But he was saying that there was some liquid coming out of his penis. It was not semen. He might have had partial ejaculation or pre cum. He wasn't sure as he later ejaculated after masturbation solo. 3. He is saying that his partner's period is due in next 3 to 4 days means the act is done few days prior to period. He is very tensed. He is worried if his partner could get pregnant. Please advise. What are the odds ?