Unless he's under 5 he will certainly remember you forever. If he's 8 or more he will surely remember your first and last name.

He will keep asking people til he finds someone who can tell him what happened to you. I don't know who, the neighbours, the landlord if you rent; when he's older he will look on the internet.

You'd be amazed what can be found for $60 on www.ussearch.com and similar sites.