As projects progress, changing directions or switching tracks becomes more and more difficult. If you identify critical decision points ahead of time, and prepare sound contingency plans and options in advance, disasters can be averted. This sort of thorough planning takes more time and may seem unnecessary, but it can save your project.
Having a vendor management system can be a big help--if you don't have one, consider creating one. Knowing how far over budget you might go if a vendor can't deliver is far better than having no idea. Stakeholder confidence and desire to follow through to completion are much more likely if they know that the problems were possible and have been planned for.
Take the extra time and effort--it can make the difference between failure and success.