The worst part of all this is that Ash will die, never having experienced actual love, imagine if you will, having lived in a world like his, completely shut off from all things but yourself, and your perception of yourself, with nothing but better yourself. No other people to interact with and issues to solve with no guiding hand.
The boy will die, never having known his dream, except as naught but a dream. The second he gets out into reality for that last moment, part of him knows it was all a lie, his faithful Pikachu? His friends? All his imagination, and maybe, he could have fought and clung to life, maybe even made a full recovery. But knowing that his efforts and ambitions had all been for naught, he just gave up and let the motion carry him away, just so he could be with Pikachu, in a place where his friends were waiting.