Are those the only 2 mods you have running?
Nope, I've got Tactics, Ease of Use, Item Upgrades, NPCKit, NPCTweak, Rogue Rebalancing, Enhanced Thief Stronghold, Hell Trials....maybe Oversight and a couple others. But I don't see how any of them could be affecting this.
You'd be surprised (or, maybe you wouldn't).
NPCKit and NPCTweak? Don't know those. (but I've been loosing track of all the mods for a while now) Only other question I can think of is: Have you run those other mods together, sucessfully, before?
Your weiDU log will list all the weiDU mods you have installed; I've long held that the more mods you have installed, the greater the potential for problems.
At this point, all I could suggest would be to load a save from before Kelsey leaves, or tries to leave, and see if he properly leaves. Or, just dump him before he's forced to leave. To get bug-fix feedback, try posting to the respective mod forums of the various mods you have installed (along with a full list of all the mods you have installed).
edit: my first choice for alternate forums would be Kelsey and NPCTweak.