If events have disappeared or you can't find them, whether you can restore them depends on your sign-in status.
Events created while you are not signed in are not synced to Google Calendar, so they cannot be restored from Google Calendar Trash.
Events that were created while you were signed in and syncing with Google Calendar may be restorable from Google Calendar Trash.
Open Google Calendar Trash from the link below. If the event is listed, select Restore.