I don't know what will spirit LW up again but I know why LW was full back in time. The former players in both servers were mostly 1990-1999 borns. Personally I was born in 1994 and I grew up in an era which perfectly connects the old and the new. It's a transition period. After 2005, the technology had sped up when compared to the past.
We started playing games with late 90s and early 2000s graphics. Every year new stuff came out. For instance look at Half-Life 1 and 2. The evolvement is A LOT. When you look at new games today, they barely differ in evolvement. So imagine playing GTA SA on your PS2/PC in a september evening in 2005. After Vice City, it's an exciting revolutionary feeling. You play it all day long. And then after this much fun alone you discover a third party mod called SA-MP. Finding out that you will be playing with other people around the world within same session. Double fun, just awesomeness. After some time you do realise it's more than a game. You make friends, chat, even learning a language (I learnt english by playing in LW).
Today's youth is served with high advancement in everything. Why would they play old SA when there are tons of other high-end games. They opened their eyes in high-tech.
To them, what looks more fun, this?
(https://www.sa-mp.com/screens/s022_7.png)
or this?
(https://i.ytimg.com/vi/2F7LcKYgXtA/maxresdefault.jpg)
To get to RP servers, I think no matter what age people are, they tend to play in SA-MP RP servers because it's the most suitable game ever for this kind of gamemode. So it's not dead yet because of that. GTA V hasn't made enough progress so far.
We gotta miss old sa-mp.
(https://i.hizliresim.com/mRqLo4.gif)(https://i.hizliresim.com/agPEgg.gif)
(https://i.hizliresim.com/Xl2465.gif)