Does it autosave even if I never pressed save?

Yes. A document is written to this browser's storage shortly after you stop typing, and again on a longer interval while you keep going, so an unnamed document that was never saved by hand is still listed in My Documents.

What if I closed the tab in the middle of a sentence?

Open the document again from My Documents. It carries the autosaved content, and a banner appears saying which time the recovered changes were taken at, so you can tell at a glance whether you lost anything and roughly how much.

Can I get back to how a file looked before I edited it?

Yes, if you opened it as a file: the original bytes are kept as version 0 in the version history, alongside the snapshots taken as you work. Restoring a version makes it the current document rather than overwriting the history.

Will clearing my browser data destroy everything?

Yes. Documents live in this browser's storage on this device, which is exactly what “clear site data” clears, and there is no server copy to restore from. That is the cost of nothing being uploaded, and the reason the export buttons exist.

Can I recover a document from another device?

No. Nothing syncs, so a document written on a laptop is not on the phone. Export the .docx and move it yourself, which is the same answer as for any local file.

Recover an Unsaved Document

The tab closed, the laptop died, or the file was never saved. What is recoverable in a browser word processor, where to find it, and how to make the next time uneventful.