What if people just keep accepting it, just not through formal banks? Paper money is worth what people think it's worth. If some money/object moves outside the banks anyway, perhaps it won't be completely worthless.
And if you can't use them for anything except real-estate purchases and the like then their value is going to decrease over time. The number of 500/1000 notes will asymptotically approach zero over time as they get converted through official or unofficial channels.