midrash - If Sarah's Death is a "Merit" for Cheshvan, Why Isn't Moshe's Death a "Merit" for Adar?

When I was young(er) I used to listen to to Toravision's Purim Story tape. (Yeah, I know, I'm dating myself.) It's a great tape, and the older I've gotten, the more it's amazed me how close the tape is to everything Chazal has said about the story.

One of the things that bothered me was the part where Haman is casting lots. Every time he tries to pick a month, the heavenly voice calls out a "merit" that the month has, which "protects" the Jews from being destroyed in that month. (This part of the tape seemed to be lifted straight from Midrash.) For the month of Cheshvan, the heavenly voice says "Sarah Imeinu Meisa" ("Sarah our matriarch died"), and Haman abandons that month, just like all the others. Apparently, Haman sees Sarah's death as a protecting merit for the Jews.

Why is the death of a tzaddik/tzaddekes a "protection" for that month?
And why doesn't Haman see Moshe's death as a merit for Adar?

Answer

Rabbi Shlomo Halevi Alkabetz (author of Lecha Dodi) wrote a commentary of the Megilla called "Manos Halevi". (It is said that he sent the book to his fiance in lieu of "Shalach Manos", since he was poor and could not afford to send her food). He addresses this question, and suggests that perhaps Moshe's death was considered a bad indication for the Jews because his death was brought about through a sin committed by them (see also the Iyun Yaakov).

Alternately, many explain (Chidushei Harada"l and the Yefeh Anaf there (quoted in footnote 25 here), R' Dovid Sabah in "Maskil Ledovid", Ma'am Loez) that Sarah's death came as a result of her hearing the news of Akedas Yitzchok and this is the merit the Midrash is referring to.

The Iyun Yaakov suggests that after Moshe Rabbeynu died it is said that "לא קם כמשה עוד" - the Jewish people suffered an irreplaceable loss, and this was considered a bad omen. Whereas, after Sarah passed away, her place was filled by Rivka.

Rabbi Yonosan Eibeshitz answers (Yaaros Devash vol. 1 Drush 3 "Veheni Oid Taam") that Haman reasoned (in his distorted understanding) that if Moshe Rabbeynu who was an expert in sorcery could do nothing to prevent his death, this is a bad sign for the Jews.