If you stop a trial of draw.io for Confluence or Jira Cloud, or you stop an active subscription, draw.io is no longer licensed.

The draw.io diagrams are stored as attachments to the pages you inserted them on (or attachments to issues in Jira), that's the only place they are stored and they remain regardless of whether the plugin is licensed.

Without a license, diagrams will continue to be viewable in both Confluence and Jira, but not be editable. Note that you hold your data in the host and draw.io is an open source application, so you can download the attachment and edit/save the diagram using the free online version or the free desktop version.

If you uninstall the plugin, the attachments remain in place, but Confluence/Jira will not know what to do with the attachment, the viewer in either product will not function.