Diablo reverse-engineered in four months, without source code

It's hard to believe that the source code of successful games is lost, but often proven true when it comes time to re-release or "remaster" classics. A recent example is Final Fantasy VIII, vanished by Square-Enix's fire-and-forget philosophy of version control and remade from scratch. Even more amazing, a single programmer spent four months reverse-engineering classic 1996 action RPG Diablo, rereating it from the ground up without the original code at hand. This video explains how he did it--and what it means for game preservation.