What happened to Kaiki in Monogatari Series?
To sum it up pretty simply,


   Kaiki lived from his attack. How he lived, and what he's been up to after that point, we don't really know.


Chronologically, Hanamonogatari is the last story in the entire Monogatari series. So, what we see there is about all we get, unfortunately.

Edit (7 April 2016): It seems there is now a "fourth season" of Monogatari novels. I don't personally know yet where these novels fall chronologically, but it's possible that more information about what happened to Kaiki could be contained in these novels.