Durons are no longer produced, that's correct.
That brings up more questions indeed. given that the heat is not uniform over the die, this bowing effect probably isn't terribly uniform either.
The article mentions variations in the order of 25 um, and 45 um. First hand, I'd be tempted to say that adding excess thermal material (see attached, red highlight) might allow the gap to remain filled, but I don't believe that that's relevant: the gap variation may add a significant variation in the TIM joint's properties (or does it??).
If I was in your shoes Bill, I'd be taking a look at your die simulator: you probably don't experience any warpage, so your tests should give a "slightly better than real-life" figures. You might be able to re-create the warpage, by capping the die with another material, but it'd have to be bonded to it, and produce the same kind of warpage... (I'm glad I'm NOT in your shoes!
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