But fear not! You can get it for free!
The reason it's dropping out is to free it up for some promotion stuff. Sometime soon after it vanishes from KDP, subscribers to my mailing list will be getting access to it for free along with a bunch of other free books. All the authors promote and all of the readers gather and snag any books that look good. You'll get to discover new authors, I'll get to discover new readers. Everybody wins!
Make sure you're signed up to the mailing list by clicking here: http://eepurl.com/ciKHID
If you've purchased the Kindle version of the book, nothing will change. This will only affect KDP. You'll still want to sign up to get the free books, however. That will only be announced to the mailing list members.