The only clue the producers have provided is that the actor
doing the voice has won an Emmy for it.
In 1992 the following voice actors/actresses shared an Emmy
Nancy Cartwright (Bart)
Julie Kavner (Marge)
Dan Castellaneta (Homer)
Yeardley Smith (Lisa)
Jackie Mason (Krusty's Dad)
Marcia Wallace (Edna Krabappel)
That was just in one year. I am reading the hint as the actor who provided the voice for the character won and Emmy and THAT character will be killed off. So in this case, Since Dan Castellaneta won but didn't win for Hans Moleman, the character of Hans Moleman is safe. Perhaps I am not reading it right.
Who else won?
Here we go:
1993:
Dan Castellaneta for Homer Simpson and Abe Simpson
1998:
Hank Azaria won for Apu
2001:
Hank Azaria won for: Apu, Comic Book Guy, Carl, Lou, Chief Wiggum and Moe
2003:
Hank Azaria won for: Moe, Carl, Chief Wiggum, Apu, Johnny Tightlips, Bumblebee Man and Cletus
2004:
Dan Castellaneta won for: Krusty, Homer, Abe, Groundskeeper Willie, Sideshow Mel, Barney and Itchy
2006
Kelsey Grammer won for Sideshow Bob
2009
Dan Castellaneta won for Homer
2010
Anne Hathaway won for Princess Penelope (not a major character)