If the link isn't on a Stack Exchange site, there's nothing Stack Exchange can do.
If the link is on a Stack Exchange site, what would you do? If you see a broken link in a Stack Exchange post, you can always edit it. This can't be done manually, you need to think about each case. Has the link target moved (e.g. migrated question)? Is there another good resource to link to? Does the post still make sense without the link?
Many deleted posts on Stack Exchange are still visible on StackPrinter. For instance, if you feel frustrated at not knowing how many favorite programmer cartoons are by Randall Munroe, you can see the thread on StackPrinter.