Hi ​@2ND WEST , Thanks for getting in touch about this!

Canceling your Professional plan will switch your team to the free Starter plan.

Upon cancellation:

• Your Professional team will be locked if it contains more than the free Starter plan's limit of 3 files and 1 project.
• To unlock it, you will need to move any excess files to your team drafts, transfer them to another team, or re-subscribe to a paid plan.

For more details, check out the "Downgrade your plan" section of this guide: Upgrade or downgrade your plan
To see what features are different in the Starter plan, take a look here: Figma plans and features

I just tested it with my own Starter team, and viewers were still able to access the file after I moved it from the Starter team's project to the drafts within the same team.

For more details on moving files, see this guide: Move a file

Hope it helps. Thanks again for reaching out!