http://revach.net/article.php?id=4689

Section: Halacha   Category: Tshuvos
Rav Ephraim Greenblatt - Waiting For A Tenth Man By Maariv
If you are davening Maariv with a Minyan of exactly ten men and one person davens a very long Shmoneh Esrei, must you wait for him before starting Kaddish?  Rav Ephraim Greenblatt in Rivevos Ephraim (3:145) says that by Mincha where there is Chazoras HaShatz you need a minyan to answer amein, however for Kaddish after Shmoneh Esrei by Maariv even a person davening or sleeping is counted for the Minyan.

The Mishna Brura says (OC 55:32) that Kaddish can be said if even more than one person is still davening as long as there is a majority.  However he says that some people are Makpid that you need nine.  If the people in question are sleeping than you certainly need nine that are awake.

Important Note: We bring this tshuvah as a starting point for discussion and not to convey any halacha.  We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. One should learn the tshuva to verify the accuracy of our interpretation.  Please understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.