Short version: your server is paused, not deleted. Nothing is lost when a pass runs out or a subscription ends.
What "paused" means
Players can't join until you add more time. Everything else stays exactly as it was: your worlds, player data, inventories, and server configuration remain stored. You don't need to do anything to keep them safe.
Your worlds stay yours
You can export any of your worlds as a download at any time, including after your plan has ended. If you decide to stop using Chunklink, your builds leave with you.
Picking up where you left off
Add prepaid time or start a subscription, and your server is available again. The world you were playing on is the world you come back to, and your friends join with the same server address as before.
If anything looks off after a longer break, ask on Discord. That's the fastest way to reach us.