I assumed everybody in the place ran out during one of the first two fights.
Explanation
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He said 'delayed' for a reason: delayed blast fireball gives both of them about three or four rounds (at most) to run. Kumo can Dimension Door away or even teleport, but the assassin has to start running then and can't waste a round killing him if he wants to live. But he also assumed the assassin would rather kill him than run, getting him caught in the explosion.
Yes, he's a psychotic moron. in a way.
To him, it's horrible to stab/shoot somebody but if they die in an explosion he figures "that's ok."