It's a possibility. When they've come through in the past it's felt more deliberate. Only specific types were let out or they were the only ones who wanted to come out. But it doesn't mean they couldn't all come through here.
If the full barrier goes down we don't have anything that can stop that. [Sad but true.] It's a big area they'd need to cover. Just getting people inside with entrances and access points blocked off would keep them safe from the things that have gotten out in the past. [The others? That could be a different story. They were intelligent. That could make them more dangerous, but also less because they might not choose to attack.]