You most certainly can be healed even if at -1000 Hps with Hide Life, you just cant be healed if your body part is destroyed and you are below -10, because you then instantly die. You must then be raised, etc. As far as disintigrate goes, I don't think it will work that way, Hide Life says if any effect would render you disabled/dying/or dead, it instead lowers you to 0 HPs. Disintigrate most certainly leaves you disabled or dead, so I would rule it the same way, but that's just my take on it. After all, if you could be -1,000,000 HPs with hide life and only be staggered, wouldnt that be about the same as being ground to dust?