The machine would have to be sabotaged to achieve some effect, but this machine only amplifies Mimi's power. She should still be able to pick things up when she isn't in it.
I asume the machine also turns her predictions into data, so Dexter can analyze it. That being said, Mimi is incapable of talking or at least, speaking if complete sentences. So even though she can still predict, she wouldn't be able to warn anyone.
In the end, does it really matter? Jeff is already dead, Mimi is already broken, Minimandy died only to be resurrected as a zombie, Halloween Town is destroyed, Dark Danny is Unleashed, Nergal is Killed and Him is no more stopped than he was all those years ago.
Yes that is true. But the focus of this comic isn't about what will happen, but how it will happened.