You can't have it both ways.
Actually you can. Exile is only temporary in situational measures. Balance on the game isn't going to make somebody impossible to get rid of, just hard. Anybody removed by the trial is going to be obv scum, so anybody returning is a priority get. The nature of this game isn't figuring out scum, it's figuring out how to permanently deal with them. As I said before, this trial isn't going to be the be all end all to the scum problem. It's going to be the start of the fight. But it's a step in the right direction for town. Instead of trying to fight all battles on all fronts, we are going to bottle neck threats as they return while finding out how to remove our last.
They would have no way to come back in time.
IIRC, the trial ends at EOD. So regardless there's a full night where threats have a chance to return to keep the game running. I had a night ability to pull any player back from exile, so if any non threats remain that aren't town and might want to watch Rome burn with a similar ability because they can't win anymore *stares at KoD*, then town probably should stay on guard regardless.