Not at all. When it’s released, you get to choose what happens. You can install the Classic Editor plugin today and when 5.0 is released, nothing will change. We’ve commited to supporting and updating Classic Editor until 2022. If you’d like to install Gutenberg early, you can do that now too. The Classic Editor plugin has been available for 13 months now, and Gutenberg has been available for 18 months. Both have been heavily promoted since August 2018, and more than 1.3 million .org sites have opted-in already to either experience, so nothing will change for them when they update to 5.0.