Usually, when you call fetchRecordZoneChanges with the previous change token, you get a list of the record ID’s that have been deleted since your last fetch.
But if you get a changeTokenExpired error because it‘s been too long since you last fetched, you have to call fetch again without a token.
For my specific application, I still need to know, though, if any records have been deleted since my last sync. How can I get that information if I no longer have a valid change token?