Planning Contigency With The Business Owners

I am running a project for a client. Today I met with the business lead to discuss potential contigency plans in case the project runs late. One of the things we discussed that I think is important is what are the must do tasks for a business area vs other tasks that they should do. For example in claims processing you must be able to open and pay a claim. Voids however can be done later. So our plan is to identify the must dosand build our contgency plan around those only.