The drugmaker has convincingly laid to rest the biggest threat to its top line.It's always a good sign when a company successfully navigates a period of uncertainty with the help of a well-executed plan. For AbbVie, (ABBV -0.42%) it looks like some celebration is in order, because it just resolved one of its most pressing issues of the past few years.Here's how this drugmaker proved the bears wrong, and why that means it's worth investing $1,500 in today.A major period of uncertainty is endingAt the start o ...