You don't manage the dependency, you manage the risk.
What is the impact of the risk? If we don't get the toilet paper dispenser installed, will the plane be unable to fly?
What is the probability of the risk? If the supplier has never missed a delivery date, the probability is low. If the supplier doesn't even know how to forge admantium, then the risk is high.
What is your risk tolerance? Building an airplane, you are pretty risk adverse. Building a $.99 iPhone game your probably willing to ship with some crash bugs.
Calculate your impact to probability score and see how it rates on your risk tolerance scale. Anything over the threshold must have a mitigation plan and should be included in sponsor status reports.
I use a spreadsheet I made for risk tracking. It has a weighted scale that gives more weight to impact than probability. Then at the start of any project I work with my team on the risk tolerance. I've had products where a score of 50 was considered a red risk and projects that a score of 90 was a red risk.