If you go into witness protection, for all purposes:

• The name is no longer in use, i.e. dead, as is everything associated with that name.
• Nobody looks for a dead man, so the safest way to protect someone who's identity must be hidden is by presuming the person is dead.
• Just like you would never reveal the new identity, seeing as that works directly against the point of protecting the person, you would not reveal that the previous identity is still alive/exists because any existing identity can potentially be traced & admitting the old identity exists reveals a potential way to find the new identity. You do NOT want anybody to even try finding them, so you tie up that loose end completely--That old identity is never to be used or acknowledged while witness protection is active, i.e. dead.

Do note that some new identities in witness protection are permanent, and thus all ties to the old identity must be severed completely & for the rest of said person's lifetime (or longer, if family is at risk).