Jester David
Hero
Normally I answer questions like this with a "it might vary from table to table" and say how I would rule. But, honestly, I might change how I rule this based on the situation.
If the druid was in a tiny animal form (say scouting as a bird) and gets blasted with a disintegrate I might be inclined to just let the damage transfer over, knowing it's going to hurt. So it doesn't ash the druid.
If the druid is a moon druid who has kicked butt the last few sessions, is near full health, and I hit it with the d-ray, I might be more inclined to have the effect kill outright. Because it's an in-combat risk.
If the druid was in a tiny animal form (say scouting as a bird) and gets blasted with a disintegrate I might be inclined to just let the damage transfer over, knowing it's going to hurt. So it doesn't ash the druid.
If the druid is a moon druid who has kicked butt the last few sessions, is near full health, and I hit it with the d-ray, I might be more inclined to have the effect kill outright. Because it's an in-combat risk.