Will my data be removed if I downgrade from a paid plan?

Our data policy for inactive workspaces

No, we don't delete your data unless you ask us to do so. As the workspace owner, the deletion of your data is at your own discretion. 

There is one exception:

We regularly clean up files from our free SyncSketch 'Dropzone' / Playground' (https://syncsketch.com/playground), where users can upload clips quickly and for free. Since this service is intended for temporary use only, we remove old files after 7 days of inactivity.