They're definitely not dead, but they have dropped in terms of activity. I remember back in the SoulSplit days numbers would reach 2,000-3,000 peak daily around the time EOC was upcoming. RSPS have been around since 2005 probably, and hit peak popularity when EOC was approaching, but they haven't, and in my opinion never will die for as long as RuneScape (in general) remains a popular MMORPG. The same reason why people play RSPS to this day is due to several reasons, but the main ones being to play a membership style of RuneScape that they haven't before, which is rare in today's day and age, but it obviously plays a factor, and since it's free it allows people to practice PKing, and in other aspects of RuneScape. Another main reason is that they want some competition within the community in terms of clans, and hi-scores that they couldn't experience in RuneScape due to how huge the game was, and how hard it would be to become relevant, or at least manage to host clan events, and other activites. My personal reason, and one of the major reasons is to max out, and begin maxed / pure PKing / gambling / staking because I couldn't experience those activities prior because I never had the time, or motivation to grind all day on the main game. For these reasons private servers will maintain relevant for as long as RuneScape is a game, and I don't see them dying out anytime soon. You also have to consider that there are hundreds of private servers, and if you accumulate the playerbase of all of them, then you'll notice that 10-20% of active RuneScape players actually play private servers (good range guesstimate imo).