The Torah is read in the synagogue only in the presence of a Minyan, as the Shulhan Aruch rules (Orah Haim 143). The question arises as to whether the reading may continue if ten men were present when the reading began, but one or more of them left the synagogue during the reading. Must the reading immediately stop, or may the reader continue until the end of the Aliya? And if he indeed should continue reading, does the Oleh recite the Beracha after the reading, and does the reading continue beyond that Aliya?
The Shulhan Aruch writes that as long as the reading began with ten men, that day’s obligatory reading is completed, even if the Minyan was lost during the reading. This means that all three Aliyot are read on an ordinary weekday, and all seven Aliyot on Shabbat, even if the tenth man walked out during the first Aliya. No extra Aliyot may be added, but the obligatory Aliyot are completed. However, according to Sephardic practice, following the ruling of the Shulhan Aruch, the Kaddish after the reading is not recited in such a case. The Kaddish is regarded as separate and apart from the actual reading, and thus if a Minyan is not present when the reading ends, Kaddish is not recited.
This Halacha applies only if a Minyan was present when the first Oleh began reciting the Beracha of "Asher Bahar Banu." If the tenth man left while the first Oleh recited "Barechu," before he began reciting the Beracha of "Asher Bahar Banu," the Torah may not be read.
Although the Torah reading may be completed if it began with a Minyan, the Maftir is not read in such a case. Halacha regards the Maftir as a separate entity, and therefore, if the tenth man left the synagogue at some point during the Torah reading on Shabbat, for example, the seven Aliyot are completed, but the Maftir is not read. Similarly, Hacham David Yosef writes in his Halacha Berura that if the tenth man walked out during the Maftir reading, the Haftara is not read, as the Haftara is considered a separate entity. If, however, the reader began reciting the Beracha before the Haftara and then the tenth man walked out, he may complete the Beracha, read the Haftara, and even recite the Berachot after the Haftara.
It must be emphasized that it is strictly forbidden to leave the synagogue if this will cause the Minyan to be lost. This entire discussion refers to a case where one acted improperly and walked out of the synagogue, leaving behind only nine men. Clearly, however, the man committed a sin by walking out. The prophet Yeshayahu says about such a person, "Ve’ozebeh Hashem Yichlu" – those who walk out suffer a harsh fate, Heaven forbid.
If there are only six men present in the synagogue who had not yet heard the Torah reading, they may invite four others who have already heard the reading to form a Minyan, and the reading may then be conducted. As long as six men – the majority of a Minyan – have not yet heard the reading, the Torah may be read. This is the ruling of Rav Haim Palachi (Turkey, 1788-1869). Although others require at least seven men who had not heard the Torah reading, Hacham Ovadia Yosef, in his Yabia Omer, follows the lenient ruling, that it suffices if six have not yet heard the reading.
Summary: It is forbidden to leave the synagogue during the prayer service if this will result in the Minyan being lost. If one person or several people left the synagogue during the Torah reading, and fewer than ten men remain, the reading may nevertheless continue, and all the required Aliyot for that day (e.g. seven on Shabbat) are completed. As long as ten men were present when the first Oleh recited the Beracha of "Asher Bahar Banu," the reading may be completed even if the Minyan was lost subsequently. However, Kaddish is not recited after the reading in such a case, and neither the Maftir nor the Haftara may be read. If the Minyan was lost during the Maftir reading, the reading may be completed, but the Haftara is not read. If the Minyan was lost when the Beracha before the Haftara was being recited, the reader continues reciting the Beracha, reads the Haftara, and recites the Berachot after the Haftara. If at least six people have not heard the Torah reading, they may invite four people who did hear the reading to complete the Minyan, and the Torah may then be read.
