Q. Dear Rov Shlit'a: On the second day Shavuot the Tefila was very long due to the reading of Ruth and Izkor. If someone had guest waiting for him to come home, (and that may create an issue of Shalom Bait) can he leave the shul before the repetition of the Amida of Musaf thus avoiding Birkat Hakohanim?
A. Poskim disagree if the mitzva of Birchas Cohanim applies also to the Yisroelim being blessed. Sefer Charodim, Hafloeh (Kesubos 24b) and others maintain it does and therefore they are not allowed to leave before it is recited.
D'var Avrohom opines it is a mitzva but not an obligation.
Horav Shlomo Miller's Shlit'a opinion is that he should not leave the shul before the Cohanim's blessing and he should explain at home that the reason for his lateness was to bring a blessing for all.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit'a.