re: If this ends up killing the Bud Light brand, what is a comparable precedent?

Tab (soda)

Tab was the first diet soda to hit the market back when saccharin (artificial sweetener) was just being introduced. After initial tests showed an increase of cancer in lab mice, the FDA mandated warning labels on all consumables with the ingredient.

Even though the risk was extremely low, consumers were unwilling to gulp down products with cancer warnings on it. Eventually the FDA pulled back but it was too late.

Mulvane is the cancer label of Bud lite