Disclaimer : The movie "Inception" doesn't belong to me
Diamond Self
The ones that leave Limbo are all changed in some ways.
Most of the time, they acquire the fragility of spun glass, a dreamlike quality that never really leaves, either seen in their sometimes slow, careful movements or the way their eyes focus on something that is neither here or there.
For some of them, it stays hidden beneath layers upon layers of here and now is all there is.
Other times, it breaks, messy and painful, and they put themselves together again, pieces rubbing against each other and not quite fitting, a phantom pain that never goes away, an idea that burrows deeper and deeper. They stay like this or...
Afterwards...there is no afterwards. They shatter under reality's pressure and scatter in the wind, never to be put back together again.
(Arthur does neither of these. He comes back burning and sharp enough to draw blood)
But, there exist a last possibility for a few rare ones, Arthur amongst them.
They reject Limbo and embrace the last pieces of reality that withstood the fall (a totem, a memory), cling to them so much that they fuse and become real in their own right ("to be is to be perceived" is rendered null and void).
(Like the transformation of graphite to diamond, the concept of self solidify under pressure)
Mal wasn't wrong to liken Arthur to a wolf, graceful, sleek and deadly. And like a wolf, he stripped Limbo to the gleaming bones and feasted upon it. He took all that it could become to him (a new reality, a new world) and clawed his way out.