We could probably still use magic to alert the town for when outsiders arrive. It might be enough to give us warning should we need to prepare for travelers. If anything else, I'm sure that we have more than enough power in this town to protect us from any possible mobs that refuse to listen to reason.
I'm curious about those portals myself... but I would advise caution in entering them. You might find one that leads to the Nine Hells and that isn't a pleasant place.