1. There was no reason for Tziporah to be killed in the war against
Midian. Although she was originally from Midian, she was obviously not one
of the women involved in causing the Children of Israel to sin.
2. I saw a Midrash about Moshe being king of Kush for 40 years.
3. Since Midian had been a place of refuge for Moshe from Egypt and from
King Pharoh's desire to kill Moshe, he refused to do the actual fighting
against the wicked Midianites, ("do not throw stones into a well that you
have drunk from")- and instead prayed for their downfall while letting
Pinchas lead the actual warfare. An interesting statement is made about
Tziporah (Sefer Hadorot): Since she was not present at the splitting of the
Red Sea (she came much later to the desert, accompanied by her father and
two sons) and was so upset that she hadn't participated in the women's
singing praises of glory at the sea, therefore her soul returned to earth
later on as Dvorah, the prophetess who sang her own special song of glory
to G-d after the war held on Mt. Tabor.
Maayan, Israel