What happens if my Supernote device isn't reachable?

Your to-dos keep syncing normally — that's the cloud, which doesn't need the device. What's affected is handwritten notes: if you try to open a linked note while the tablet is offline, the app shows the last copy it saved rather than stalling. For a note it hasn't saved yet, it offers two ways forward: turn on Browse & Access (recommended — gets the latest ink) or download the note's last-synced copy from the Supernote cloud. The sidebar connection item shows the device as disconnected, and the app keeps quietly re-trying to find it, so the moment you switch Browse & Access back on (on the same Wi-Fi) it reconnects and catches up on any notes it still needs.