Zok had never stepped a foot out of the Wilderness, not had he expected to do so ever. But thanks to Naalnish, he was forced to do the unexpected. Sofina sent him out of the Wilderness using the last bit of her magic before she disappeared... just like Adrion.
Zok didn't know whether she was gone forever or just waiting somewhere to be resurrected. He was hoping for the latter because Zok did not want to think someone died to help him. As for Cero and Kaira, they were stored safely within the Book of Master Tamers.
As soon as Zok had placed the creatures inside the book, the book itself integrated with his body. Meaning he could summon Cero and Kaira in and out of his body upon will. As much as Zok hated that his pets were not around him all the time, he found solace in the fact that they were still safe within him.
