They've already started dropping, they also aren't keeping up with inflation. More GP comes into the game, and it's been sitting at 200-250 for a while.
I've also seen people selling them for 200, and desperate buyers paying around 220-230. Was around 250k around a week back.
Im seeing people buy them 350k each
This is a tough question... Although the supply of zamorak pages will increase so will the amount of gp in the game. So no one really knows but I think they will defiantly decrease as people calm down and stop buying them at such expensive prices

