What happens to my subdomain if I cancel?

It stops serving your page once the account closes, and the name eventually frees up for somebody else. Rejoining soon after usually recovers it, so tell us before it is gone if the name matters to you. Two things worth knowing in advance rather than afterwards: if you had connected your own domain, it stops reaching us as well — the domain stays yours at your registrar, but there is nothing on our side for it to point at; and every QR card and shared link you have printed runs through that address, which is the real cost of letting it go. Nothing about the address changes while the account is simply paused.