well in SDF Macross Misa, Hikaru, and Minmei were teenagers. by the time of frontier they would be in their 60s? i think they could safely use different voice actors safely.
P.S. if we can't see or learn of Misa, Hikaru and Minmei's fate can they at least have an extra 5 minutes at the end of the last episode of frontier showing Kaifun dying a slow horrible death? i'm watching macross again and i am really starting to remember why i hate him so because he is a huge @#$hat.