A pre-generated island could be a better idea, and it would only begin generating if you were to dig down. That way, you don't have to worry about running out of bricks, unless there's too much underground mining.
I assume that the gamemode would have restarts to stop from brickcount overflow, like unlimited mining. If you wanted to, you could have an emigration timer in which all the people must gather resources before the emigration time reaches. When the emigration time reaches, a dragon or something boss related that is nearly un-killable will come through the lands and ravage them to make sure everything is destroyed. Say you were to kill him, you'd be awarded heavily, the world would reset to a clean one and you'd be a rich immigrant in the new world. If you die in the boss stage, you lose everything. You're basically taking a risk.
I don't think you're taking suggestions, but I thought this was a creative approach to your brickcount issue.