A sense of impending doom is a feeling of knowing that something life-threatening or tragic is about to occur. Sometimes starting fresh is either not possible or not the right choice. If a project is in midstream and could benefit from Scrum, it is good to switch. It is good choice to pick a pilot project that are currently headed toward impending doom yet still have enough time to recover and succeed.
Although this can be a risky approach to pick a struggling project that has nowhere to go but up. Delivering at all is often viewed as a success, delivering on time is often viewed as an amazing success. Because of the focus and intensity created through working in short sprints and because of the emphasis on creating at least some forward progress. Scrum is ideally suited to these types of projects. It is good to have an experienced Scrum Master or consultant who can guide or steer the project to achieve success and coming out of impeding doom situation.
Book: SUCCEEDING WITH AGILE Software Development Using Scrum by Mike Cohn