Kemmler still has four of the Nine Books of Nagash right?
"A Bonestrewn Path - 7" didn't seem like Kemmler currently had access to his four Books of Nagash, but that might just be because he left the books in Mannfred's Observation Tower.
He still has his books, that's what his mobile undead ogre bookcase is for. Basically kind of like a Mortis Engine that's got legs and can be a bit more subtle than an enormous spooky Dark Magic floating ship/chariot thing. Arkhan was more focused on actually straight up killing him rather than taking the books and running away, because both of them are supremely arrogant necromancer people. He wasn't going to try and just scurry in and yoink them, he was going to kill the pathetic mortal that dared to gather them up, and also to wrest control of Krell for Nagash's purposes. In the process, all of Kemmler's forces were destroyed or dominated, but he barely managed to escape whilst ravaged physically and mentally and also with his soul scarred by Arkhan's superior magical power and knowledge.
But yes, he has his books, but he's also got other books and some of the stuff he stole from the Sorcerer's Islands. The reason he was in Mourkain is because it's a far greater locus for Dark Magic, which is part of why it was built their originally, whereas the tower that he has claimed for himself that used to be Mannfred's secret observation post is deliberately out of the way and not particularly in a place of major magical power - lest others seek it out and sense a huge wellspring of Dark Magic that they'd want to claim. The tower is a sanctuary and place of study and secrecy. Mourkain is a place of power, and Kemmler was feeling confident about hanging around there and summoning more spirit hosts to his side, building up more undead forces, experimenting with the greater Dark Magic drawn there, etc.
Then Arkhan booted his ass from one side of Mourkain to the other, nearly killed him, and now Kemmler has yet again been forced to try and rebuild his forces and most importantly his actual health and strength in all three categories - body, mind, and soul - after the sheer damage Arkhan did to him. He still has all of his book, but he did lose a lot of scrolls, time, servants/slaves, etc.
The thing about Kemmler atm is that he's not willing to be parted from the Books. He's quite certain that if just left them alone, all four together, that someone would come and grab them. Like Arkhan did, because he sensed four of them at the same time in close proximity, and Arkhan has a particular connection with Nagash and his stuff. Not enough to stop the Crown of Sorcery getting thrown into the Realm of Chaos as a sacrifice, but that was a rapid thing when it was done and also Thorgar had an enormous horde around him with lots of force that would have crushed Kemmler in comparison, so Arkhan couldn't be so certain he'd win.
Arkhan cannot easily move in and out of Nehekhara, he has to be careful and measured about it, because if he's ever too far gone from position, he knows it's likely Settra will come and do thing that Arkhan would very much like him not to.