One who has a nocturnal emission:[1]

Must worry the entire year: One who has a nocturnal emission on Yom Kippur should worry the entire year regarding whether his fast on Yom Kippur was accepted.[2] [This however only applies to Tzaddikim and men of stature, whom do not have erotic thoughts which can lead to nocturnal emission. However, an average person who does have erotic thoughts, should not fear a nocturnal emission, as it is due to his own actions.[3] Nevertheless, as a Tikkun for this matter, one should recite chapters 103-104 on every weekday until the next Rosh Hashanah. This does not apply on Shabbos and Yom Tov.[4]]

If survived year then will have a long life: One who experienced a nocturnal emission on Yom Kippur and went on to live through the year, can be certain that he will receive a portion in the world to come, as he certainly has many merits which protected him. He will also live a long life, as an emission of seed is a sign for living long years.^[5]

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[1] Admur 615:2

[2] The reason: As perhaps by Hashem giving him the pleasure of having an emission is a sign from above that his self-imposed oppression of fasting was not appeasing, and therefore he was forcibly made to have pleasure in something else. [See Admur ibid]

[3] Tzemach Tzedek in name of Alter Rebbe brought in Miluim 64 Choshen Mishpat [and Orach Chaim 111]; Piskeiy Teshuvos 615:1

[4] Igros Kodesh 4:58; Shulchan Menachem 3:174; See Piskeiy Teshuvos ibid

^[5] This corresponds to the opinion brought in Tractate Yuma 88a that having a nocturnal emission of seed on Yom Kippur is a good sign which shows that the person is a Tzaddik. See also Or Torah of the Maggid [Torah 209] in the name of the Baal Shem Tov that if one sees a nocturnal emission without having triggered it with bad thoughts during the day, then he is not to worry of it. On the contrary, Hashem made him have it in order to save him from death, as the decree of death was expelled through his seed. See there!