As people have said it, if no one buys rares their prices will go down because of the amount of people desperately trying to sell them at lowest price to get some cash for items that you can actually use and not just show off. The rares will eventually die out of course because of the amount of people quitting without selling them in case one day they come back in the game, or simply getting banned with them. But for the reason i stated above i don't think that the price of rares will ever go past 800m-1bil, every time it reaches its peak it will just go back down the next week.