I mean you can repeat it with a hypothetical version of IB that's decoupled from Defiance, and no Grit on the DRK.

In that case, the WAR is healed from 42760 to 48750, then takes 40000 damage after the IB reduction, winding up with 8750 HP.
The DRK's shield reduces the hit from 50000 to 38600, leaving the DRK with 4150 HP.

If the tankbuster is bumped up to 60000 damage, the WAR survives with 750 HP, and the DRK is dead.