Or maybe it becomes void and a new random player is given a new scroll on the next day? That or they just stack up I guess.
I mean maybe in the beginning an extra role could be helpful, but towards the end, it could throw a sea-monkey wrench into a town block's plans, unless it's a ability that can do no harm like a protector role. But hey, even that could do harm if we have for example a vigilante. Now if the Traveler was in the town block that could be a different story, but we don't know what their win condition is, so they couldn't be fully brought in.