Unsurprisingly, Blizzard want to keep that train going for as long as possible. They are in this for the LONG game. Speaking to GameSpot, Blizzard Entertainment executive producer Hamilton Chu said that the company hopes the game will be around for decades.
We want Hearthstone to be around for 10 to 20 years. That's what Blizzard does.
He recognized that the longer things go on though, the game does face one major problem. The more time that elapses, the more cards are added, and the harder it gets for newcomers. When asked if this means that old cards might one day get culled, he respond:
I mean, I don't know. This is something we're going to have to figure out how to manage and how to address in the long term. There's no easy answer.
I can't imagine taking away cards would be a hugely popular choice. People are obviously sinking a ton of money into their decks and to one day potentially lose the cards in them… I just can't see it going over well.