Dice sites will probably die off eventually especially when the market gets saturated. I think they need to do what I heard PrimeDice are doing and expand by adding more games. Dice is pretty simple so it's ok to play occasionally but I'm sure people are more interested in other games that they could play and go back to dice when they wanted.
Depends. Dice is a fast game with simple rules. And offers immediate results. Lots of people like that. And prefer it to more complicated games that need more time. No wonder dice games haven't disappeared after existing for 5000 years. Maybe sites having more games helps. It certainly brings in more players. But I doubt good dice sites will ever die off completely.