Actually yes, they are dying .
Even though Bitcoins is not at its best since the beginning of the year recent news has confirmed that NOW 54% of all the crypto currencies in the world is Bitcoin , which pretty much explains the story of Altcoins doesn't it? .

 Altcoins are dying also because of too much production and many ICOs burn some of their coins ( for its good only) . This may also be a reason for its decline.