Your content is not destroyed when a plan ends. What changes is how much of it is shown.
- Listings beyond the new limit stop appearing publicly.
- Images beyond the new per-listing limit stop being shown.
- Events, deals and menus stop showing if the new plan does not include them.
- Bookings stop being accepted.
Upgrade again and it all comes back. Nothing has to be re-entered.
Before downgrading deliberately, decide which listings matter most, since you do not control which ones are hidden.