Actually when you think about it, when it's defenses are fully up as presumedly they are now that the island has a Warden again, there shouldn't be any Ways open to Demonreach. Because a Way that can be easily opened leaves the island vulnerable to invasion. When Rashid and Peabody used it, the defenses were not fully engaged, yeah, Harry had just become Warden, but he had no clue he that he was or what it meant. Still even then the one Way wasn't easily used. So Alfred might be able to give Harry a special key for travel through it now, but I bet that Way is now closed even to Rashid.