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The only thing that keeps a reference to the collection is the OtherView instance. You just need to make sure that no references to the view exist. The garbage collector will collect it when it deems appropriate.

The view's element in the DOM will prevent it from being collected by the garbage collector. So, as you know already, calling remove on the view or manually unbinding everything (events from jQuery, Backbone, and native in addition to any references) is necessary.

The models, when added to a collection, automatically keep a reference to the collection if model.collection isn't set already. So if they came from another collection, the models won't get the new collection and all is fine, just keep that in mind as it could cause a problem someday.

[...] can I rely on JavaScript to remove pageCollection [...]

I would say yes because anyway, a Backbone collection doesn't have a delete function. With JavaScript, you don't really need to keep track of objects and explicitly delete them. You need to keep track of the references and remove them.

It's good to research the possible memory leaks problem in advance, but it's also best not to fall into the infinite hole of premature optimization. When you'll get a leak where you can't find the source, or just don't understand how to fix, come back to SO and ask about that.