I dont know if anyone else has this issue with the offline version of the game on PC, but I recently found a solution. 

Typically what happens is after a while the game starts to play like a slideshow, and if you keep playing it eventually locks up. If you launch task manager, and the look at the details of the exe, and then analyze the wait chain, it will say something like warhammer.exe is waiting for network I/O and it gives you a thread number. If you download sysinternals Process Explorer and then look at the threads running for Warhammer.exe, and find the thread number that correlates with the wait chain that is hung up, and then kill it. So far the game doesn't crash, and the choppiness goes away. I can keep playing. So who ever found the solution on Steam thank you, it works for me, and I can keep incinerating the enemies of the Imperium. Still dont know why the offline version of the game needs to access the network or why its always the network I/O that hangs, but whatever the temp fix so far works and I am glad. So anyone else having the offline version of teh game be choppy then locks up on em. Analyze the wait chain, and pay attention to the thread number that is stalled, and open process explorer and double click warhammer.exe and look at the threads tab and kill the thread number. See if you can go back into the game. Hopefully it'll stop being a slideshow for you.