This was published in The New Hacker's Dictionary compiled by Eric S. Raymond, second edition 1993 (and probably in the first edition), so it's been around for a while. I'm sure many here on the forum have heard it.
The question of if this person called Mel is still out there isn't much of a question to begin with. It's been about 50'ish years since the alleged event of Mels development of the blackjack game, so chances are that unless he's found the fountain of youth then he's pretty much dead or on his way there. In addition, this is a C++ forum, by the description of Mel in the story he most likely wouldn't even touch this forum let alone this site with a 60 terabyte long e-stick. The story it self doesn't seem to have much documentation to support it either way.
I will admit that I've never heard of the story before this post, and I do in fact find it quite lovely. It's an amazingly cool story, so much so that I do wish for it to be true. So inevitably as I grumble stumble ramble scramble my way through typing this sentence I'd like to say "LONG LIVE THE STORY OF MEL", because I'm seeing that this(My) post has no real value behind it. But I'll hit submit either way.