The situation according to StoryMaps.com support is as follows:
"If you request account migration by May 31, 2025, you will be offered the choice between a free subscription to a personal, noncommercial version of ArcGIS Online (an ArcGIS for Personal Use subscription), or a subscription to ArcGIS Online that allows you to create stories for commercial use (a Creator user type subscription). This free subscription will start in June 2025 and end on July 21, 2025. When the free subscription ends, you will need to purchase an ArcGIS Online subscription to continue using ArcGIS StoryMaps and accessing your content.
The ArcGIS Public account will not be an option if you’d like to port over your existing StoryMaps account and content to ArcGIS Online. However, you can sign up for a new ArcGIS public account at any time or use ArcGIS StoryMaps with a separate public account. Please note that some advanced features and capabilities in ArcGIS StoryMaps are not available to public accounts, and there will be more limitations compared to the free basic plan in StoryMaps.com."
So as I understand it: If, like me, you make maps on a voluntary basis for third-parties, like charities or volunteers organisations, you'll need to pay for a Creator license after StoryMaps.com closes down, or you take your chances and re-create everything using an ArcGIS Public account and hope ESRI don't close that route off for free map sharing too in the future.
