The app will dissapear since no one has access to it.
You can switch the source model to the page via Page settings or manage models on the App page. But you have to do it before the archiving and have another model with the same structure as the initial one.
You can link multiple models to a page (can be done in page settings).
If a model moved to another WS - for anaplan it is a copy of the original model - it has new model id and the URL - even datacenter can change. This means you have to link this "new" copy to the app manually.
