The borders of the 16x90x16 space he's trapped in are indestructible invisible blocks. He cannot place blocks against those invisible blocks, so if he were to destroy everything in there, he will not be able to place any more blocks.
It is completely dark except for light sources he places.
We don't know for sure what dimension he would respawn in if he died, but he cannot die anyway, because he cannot access any void or change himself out of creative mode. OP powers would allow him to suicide, or possibly use some other command to change dimensions (Mystcraft has /tpx. Maybe AE has something, too.)
He cannot be rescued from the outside because the storage cell he was in has been destroyed.