Great question, it came up right away so there is an old discussion that you can find somewhere, but I can't remember what post it was on. The two suggestions that I preposed then were increasing the decimal precision or using funds in the @proofofbrainio account to continue the rewards system. I also pointed out that proofofbrain.io is not necessary for the coin to survive, it's just the distribution mechanism and all of the wallet features exist on hive-engine.com and powered through the Hive blockchain. Of course it's hard to say what that will look like in 2155.