ok so i just got back from seeing the new harry potter movie right and it was great, except i dont understand the ending

. im very very frustrated...
i dont understand why voldemort didnt get killed i mean understand that he went poof and you know went somewhere else but i thought there wasnt going to be another movie and i dont understand how they can make this movie without him dying if theres nothing to happen afterwards i mean whats going to happen???? are they going to have a different cast?? ugh
help!!!