It's an exponential function. Runescape 07 will continue to decrease but in smaller and smaller amounts.
Pretty simple stuff: assume 1% of 07 players quit each week. That 1% keeps getting smaller as the player base shrinks.
It'll never TRULY die, but it will keep decreasing until it's impractical to continue PKing in it.
This is something I've thought about since before the implementation of it, and I am still thinking about the future.
RS3 is also shrinking.
What do we do? Just let things unfold for now and rely entirely on Jagex. They have a bad track record but they have also kept the game going for 13 years.
So we'll see.