Actually I meant the hammer is pretty lame. It is only level 5 so you'll probably not want to use it for long (if at all) as most likely you'll be level 5 or 6 at this point anyway.
Why it only drops sometimes drops I don't know. Usually when you get either Dallis or Alexander to zero HP they fly away. Sometimes she drops the hammer sometimes not. If you reload to just before the final shot that takes them to zero you can repeat this until the hammer is dropped.
I have had Dallis go to zero and just carry on fighting indefinitely though. Each turn she would regenerate a little HP through some unknown mechanism, not healing, not necro. After getting her to zero about 20 times I gave up and left the fort as that gets rid of her but without the XP for her flying away.
