Is there a way of replacing the deleted playlist items that you lost when removing duplicates with the one copy of the track you kept?
Maybe it's just me, but I don't understand the question, or what MrC thought it meant. ?
What are you removing duplicates
from? If you what to play a playlist intact, there's no need to remove anything. If you want to remove duplicates from a smartlist selection, then it doesn't matter which copy of a duplicate track is played.