I'm not sure if this is a question for philosophers or for physicists, but I'll
Let's use a phrase from the philosopher David Lewis: concrete worlds. Let it mean complete, concrete universes. Lewis thought that there are concrete worlds other than our own, and that there is at least one for each way our world could be. Lewis also characterizes these words in the way you do: they aren't in our space-time, so they're not at any spatial or temporal distance from our concrete world, and they don't interact causally with our world. As Lewis understand things, they wouldn't be other worlds if these conditions didn't hold.
Lewis thought there were such things. He thought that making sense of ordinary truths about what's possible calls for them. My admittedly unpopular view is that this is the wrong way to think about possibility. Even if such worlds do exist, there may be (would be, I'd say) non-trivial modal truths about them. Any particular such world might not have existed, for example. Far as I can see,here's no home in Lewis's account of modality for these sorts of possibilities. In fact, I'm tempted to resurrect an old term and say that the Lewis-style way of thinking about possibility amounts to a category mistake.
But that's just me, and at least some of my colleagues would hoot in derision.
Be that as it may, it's one thing to say that these worlds would be the wrong sorts of things for the job Lewis assigns them (and I realize that's not your issue); it's another to say they couldn't exist. I can't think of any good reason to believe that such worlds are flat-out impossible. And though I'm open to persuasion, my instinct is to suspect that any "proof" to the contrary would be sophistical.
This might sound like a simple "yes" to your question, but it's not so simple as that. What's possible and what I seem to be able to describe or imagine may not be the same thing. It may be that, for reasons I'm not grasping, utterly other concrete worlds are not possible. All I can say is that if I were making philosophical bets, I'd go with saying they are. I'm just not sure what my odds would be...