While many major characters are dying, there are still many left to face, including:

Agamaggan (Possibly)
Al'Akir the Windlord
Anub'Akan
Arthas
Azshara
Black Riders (from Deadwind Pass)
Deathwing
Hakkar the Houndmaster (Possible CoT boss)
Jin'zakk
Kael'thas
Kel'Thuzad (Still not dead yet)
Kil'Jaeden (the likeliness that we'll actually kill him when he's half-summoned in Sunwell Plateau is really low...)
Malygos
Mannoroth (Possible CoT Boss)
Murlocs
Neptulon the Tidehunter
Old Gods (Three Remain, and C'Thun might not be dead)
Rokhan
Sargeras (of Course)
Therazane the Stonemother
Ula'tek (A Loa Similar to Hakkar the Soulflayer)
Whoever the Leader of the Makrura is

Ok, that's a few. We will probably find out that Illidan isn't dead as well or soemthing.