No, it will rupture at some point.
This is extremely unlikely. I'm not going to say it's impossible, but I don't think it's going to happen. I know there was a case report shared here regarding an infant with purported cranial rupture secondary to hydrocephalus, but I find that paper dubious for multiple reasons. Basically, almost everything published right now is shit and you should regard it with a healthy dose of scepticism.
What's far more likely to happen is that her remaining brain will herniate due to increasing intracranial pressure, causing her body's most basic functions functions to cease. I hesitate to say "die" because I don't really think she's alive; her body is just trucking along because it's what we have all been evolving to do for millennia.
I don't think she has much cortex left at all, and I suspect that the deeper structures remaining are deteriorating by the day. These brain structures are responsible for autonomic functions like heart rate, breathing, sleep/wake cycle, and regulation of blood pressure. Humans, especially infants and young children, can lose a lot of cortex without any really serious deficit being apparent, but once you start talking about damage to the midbrain and brain stem, it's a totally different story.
This is a pretty typical manifestation of multicystic encephalomalacia, with severe damage to the cortical structures and relatively sparing of the midbrain and brain stem. In a way, this is almost the worst possible outcome of a brain injury - being "alive" because the primitive parts of your brain haven't yet realized that you're dead, but having such severe global damage to the cortex that you have no consciousness. Incidentally, I suspect that there is probably not enough cortical tissue left for anticonvulsant medications to be effective for Luna, even if Robyn were to allow her to receive them. This is something that I mentioned a long time ago, but seeing her movements in recent clips has brought it to mind again.
Like anyone else, I don't know when the end is going to happen or what exactly it will look like, except to say that I think we've been watching her gradual decline for months now. It's important to keep in mind that all of Luna's other organs are perfectly normal and healthy. She doesn't have an underlying genetic disorder or an illness affecting other organ systems. Who knows how much longer her body can keep going.
In a philosophical sense, I don't know why she's still alive other than because our universe is a fundamentally absurd and sometimes very cruel place.