A demanding enough PVE system can produce the same demand, relative to the level of active players - unlike many other MMOs, etc. you don’t just respawn with all your gear after wiping in a raid and so on.
I don’t see the game holding the same activity level purely on PVE though - most games which try it tend to drop down to around 4K active players for the long haul or drop to very low levels if there isn’t continued investment in new opportunities from the developers i.e. look at The Division.