I like Kerrigan going through a redemption arc for at least two reasons
1.) Blizzard has done the fallen hero routine many times, and almost all of them end up dying and going to hell (Arthas dies at Tirion's hands, the dark wanderer is consumed by diablo after being made into a host, Illidan became loony, Kaelthas....). Having a hero climb out of the darkness and achieve redemption would be new and could be genuinely compelling and engaging.
2.) Kerrigan's life has been tragedy after tragedy ever since she was 8 years old, so she deserves to finally find some solace for her past. Even if she's not happy she deserves to be able to lay her past to rest.