With all of these I think it depends on the severity of the deviation the failure causes to the original scope of the project. Sometimes losing a vendor or a new regulation might not have a available alternative or work around and the project cannot proceed or must make drastic or time and money consuming changes to continue. In cases where there are alternative solutions like failures with vendors, a company should have backup vendors in mind. Perhaps their first choice was merely the most cost effective and the project can continue using the second best deal. New regulations must be examined for their effect on the project and if the change is minor can most likely be worked into the project without detrimental amounts of delay.