I am a bit confused. If you spent 80K miles each then you are spending for Business award seats. Now they are not available and all they can do is put you in economy and waitlist you for the business class seats which you have already been charged for. That should be why they gave you economy plus seats. If you want an economy award and have status they would put you in economy plus seats for the miles of an economy award. If you don't have status the only way you could get economy plus is to use the miles for a standard award which is considered a full fare ticket. As you have used the miles for business awards but they could only seat you in economy and waitlist you for business then there should be no change fee as you have already "paid" for the business class seats. If your waitlist does not clear then you would get back the miles difference when you leave, but only if both directions don't clear. If you fly one in business you have flown the whole thing in business as far as how many miles it will cost.

Please correct me if I am wrong on any of this but I am in the same situation with awards to Australia and this is how they explained it to me as the business class seats are not available yet.