Sadly, if you cannot log into the account that is linked with your bungie.net account, then it's stuck there. Bungie will not adjust or mess with linked accounts or their links to the bungie.net profile they're linked to; you have to do that yourself, and if you've lost access to that account, then you're out of luck. You could speak to Blizzard support concerning making that account temporarily available one last time so you can log into it concerning this since it wasn't something you probably should have forseen beforehand, and you can use the knowledge that Bungie will not adjust links, no matter what kind of proof you throw at them saying you're the proper account holder. It's their policy. Maybe Blizzard will be kind enough to help you out with it considering all this. Good luck.