No one here has given the correct answer unfortunately.
Let me give you a brief history of RO (I've played private servers for roughly a year, and the game since it was released)
The original RO was released in the late 90's, but not to the US. Around 2002-2003, iRO was released. It was EXTREMELY popular in Korea, Japan, and England (Go figure?). The game was actually one of the most highly played games in Korea, and believe it or not, they signed a deal with Domino's Pizza to put an NPC into the game which you could enter your credit card info, address, and your order, and they would deliver it to you, I'm not s*** you.
RO was a huge success. There are, literally, millions of players believe it or not, mainly in countries other than the US.
The real iRO servers have about...100k people on them. Due to the lack of player body and utter failing of RO2, they've started to focus on RO again, as with the addition of the kafra shop, 11.3, etc...
Private servers? They make up a small fraction of the RO world. I've guesstimated, by using charts from server listing sites and connections, that roughly 30 new US private servers are made daily, and about 5 die. That doesn't sound so bad to me.
Despite what you may think, and what it looks like, RO is an extremely huge game, with even more players than Diablo II, which is huge.
This game will never actually die, unless computers advance past it somehow. Gemstone 3 has been around a hell of a lot longer than RO, and its stilled around with a few thousand actually PAYING for it. It is extremely rare that a game EVER dies completely. A game never loses more than 1/4 of its maximum player base, because its the cycle of life. Those who die, are replaced by those who are born. People who leave the game out of bordum, will be replaced by those who have never played and seek enjoyment.
Ragnarok is one of those games that, no matter how crappy the graphics may seem at times, or how old it is, its an enjoyable, fun, and action filled game. Thats, personally, all I really care about.
If you really asked me, in my heart of hearts, how long it would be around? 70 years. Games are the books of the future. No matter how old the get, people will still play them. My guess is 70 years since, by that point, computers may actually have trouble reading such an old script.
That is my sensus of the entire matter.