A DeadLink can be repaired by finding an archived version of it. The InternetArchive?'s WaybackMachine? usually has archives for old links. However, the archive isn't a complete collection of the internet, and as such some dead websites won't have any archived versions at all, and may be dead forever.
We can prevent DeadLinks from happening in the first place by archiving it now. When you read something and want to link to it here, it's a good idea to archive it first, so that when it goes down, you will always have a working copy of it.