Your site is yours to keep. Export it as code, archive it when you need a free slot, or delete it when you are done. Here is what each does.
Code export is an Ultra feature. It downloads your site as a Next.js project you can run or host anywhere.
The zip is named after your site. It contains the project without BYQ's editor files, plus a README with two parts:
On other plans you see “Exporting code is an Ultra feature.” If you have not built anything yet you see “Nothing to export yet. Build the site first.”
The README includes a Hosting it yourself list. BYQ hosting adds some things when it publishes, and these are not inside the exported code, so set them up again on another host:
Archiving frees one of your sites without deleting anything. From the site's card, choose archive and confirm Archive.
A site with its own $15 a month hosting needs the hosting cancelled first, so you do not pay for a site that is offline. Use Settings and Manage hosting.
Restore an archived site any time you have a free site slot. It comes back as a draft: publish it when you are ready.
If you downgrade and have more sites than your plan allows, you get an email, “Your sites are over the [plan] plan's limit”. After 14 days the least recently edited sites are archived, and a second email tells you how many. Sites on your own domain do not count toward this. Nothing is deleted. Upgrade or archive sites yourself first to choose which ones stay.
Deleting is final. Settings explains it before you confirm: the site, its chat and every version are deleted for good. The site goes offline, a connected domain is disconnected, and any $15 a month hosting for it is cancelled. If you only want it offline, unpublish or archive instead (see Publish and keep a free site online).