Once you have flagged the question as a duplicate, leave it alone for others to do their work. It will remain open for answers until the question is closed as a duplicate. If you think the answers are an exact duplicate of the answers posted on the original question, flag it for moderators' attention.
Moderators and >10k users will see if the answers posted on the duplicate question is exactly similar to the answers on the original post and may delete it if they find that they are exactly the same.
IMO, downvoting should be used only if you think the answer is useless for the question in consideration. Flags are appropriate here.