Note that it looks like a persisted grant can be restored without opening a file picker for the lifetime of the process that obtained the grant even after you have disposed the grant.
After the process exits (the app is restarted) the grant is permanently gone until the user explicitly picks the file again.
Per discussion here: https://github.com/hpoul/file_picker_writable/pull/19#issuecomment-819555749
Note that it looks like a persisted grant can be restored without opening a file picker for the lifetime of the process that obtained the grant even after you have disposed the grant.
After the process exits (the app is restarted) the grant is permanently gone until the user explicitly picks the file again.