Originally Posted by
Sevyvia
I'm guessing his (reasonable) assumption is that boss health is stored as a signed int variable, which goes from -2,147,483,647 to 2,147,483,647. In other words, max boss health = 2,14 billion. Even if it's stored as an unsigned int for some reason, it would be postponing the problem to around 4,3 billion.
Of course, Blizzard could've had a moment of foresight back when this was built and put health into a long or something, which would mean we won't see the cap any time soon, as an unsigned long foes from −9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.