Maxperson
Morkus from Orkus
they had this debate over on WotC a while back. Disintegrate is nasty because it screws up the corpse. But if there's a pile of you left when reduced to zero from an attack, then you can revert to heal, i think. Disintegrate also has a damage value, so if the type of shifting you have done says you 'heal' by shifting, in theory, the damage could be compared and the remainder carried over. But perhaps Disintegrate has the special effect of saying 'dust is dust', making it one of the most deadly spells in the game.
The issue is that the druids wild shape hits 0 before it transforms back and the disintegrate dusting effect triggers on hitting 0, not at the end of the damage being dealt. By RAW, that avoids the requirement that the damage carry over to the druid's normal form. By RAI, it should carry over before being turned to dust.