Also, a question. If DiCaprio is indeed dreaming at the end, then he won't wake up, will he? It was my understanding that somebody caught in limbo would spend so long dreaming that they would live a full life and "wake up" a complete vegetable. In other words, DiCaprio will have his life with his children and then, at the end, die.
The idea is that while in limbo you, as I understand it, cannot die. He and Mal had lived a lifetime
there something like 40 or 50 years -long enough to be old and gray by the time they ended it. But limbo does
leave your "real world" body comatose and the length of time it's like this could be days, weeks, months or years or until your body dies/is taken off life support. So when you do
wake up you'll have all your faculties -as he and Mal did after a fairly short time passing in the real world- but if ages pass in the real world it's possible that your body will be disabled, like how if someone were to wake up from a PVS they'll mostly be mentally capable but their body will need rehabilitation.
So if at the end Leo is still "in Limbo"/a dream he could someday wake-up and still be -mostly- mentally sound but his body may not be up to snuff depending on how long he was in a PVS, and they be a bit disoriented -as Picard was when he woke up at the end of The Inner Light.
But he would wake up and likely have most use of his mind depending on how badly his brain was messed up during the coma he'd be in during the intervening time.