If he had a usable EmuNAND, he could have already restored that to SysNAND.Maybe you can try to boot an emunand...
The problem is that the N3DS downgrade to 2.1 does weird voodoo bullshit to the NAND to make it work that is apparently not undone by GodMode9.
I'm not sure why Decrypt9 isn't working, but it sounds like d0k3 is working on allowing GodMode9 to fix this issue.