Is it just me or is that spell like crazily badly written? As Phaedrusxy noted, it's instantaneous. So, how can the spell "end." Can it even be dispelled? It still functions in an AMF, too, doesn't it?
It also would help if they explained the way healing worked a little better. I think posters above me are correct: you can be healed normally until you are "dead." And, then after that, no healing. But, it could be spelled out better. That being said, Delay Death would give you plenty of time to climb your hit point total back up in practice.
As a side note, 2E had a spell nigh identical to this, I think in the Arabian setting. It was obviously a Sinbad riff, and you just hid your heart away and couldn't be killed with hit point damage while it was intact.