Check the poster's profile to see if they are still active on the site. If their profile says they are inactive or if they have been offline more than 30 days, just post in the thread that the links are dead and the poster is inactive. Moderators will take it from there to let active reposters know it's available to be reposted.
If the poster is still active, please contact them via PM to request a re-up. The PM button is found on the bottom left in the classic version of the site and in the 2.0 version it is found to the left panel under the user's info and looks like a word balloon from a comic strip.