In some cases, there may be no way anymore to access the information, but the LEGAL file may still need to document where we got the information from. That means that we may need to keep the dangling links because we have nothing better. Maybe we can add something like "accessed at DATE" or so.
In addition to that, perhaps for links that may no longer exist, one could mention the year where it last worked or so, just as a rough guide for people who may want to find out when something became obsolete (I mean the link itself).