Not necessarily. The hardest part of any dissertation to write is the original stuff - your own analysis and discussion. So often, students spend their time on the lit review and methodology and neglect the analysis and discussion - so my advice is that get working on these - so you must make a decision on that additional case study - you say your supervisor shot down your suggestions, so I would go back to them and have further discussion (you need to take something with you to that tutorial obvs).