What does it mean for DataFrame.ix to be deprecated?
That's the basic idea of deprecation. The library's maintainers are letting you know now that they plan to stop supporting ix (e.g., fixing bugs in it), and may very well remove it in the near future. As long as it's deprecated, you have a window of opportunity to change your code to use other alternatives (such as loc and iloc), on your own terms, before you're forced to do so when pandas breaks "under your feet".
Suppose I use DataFrame.ix in some code.
Does the fact that it's deprecated mean that at some point in the future, I'm going to update pandas, and then a little bit later, the stuff using that code will mysteriously start to break because they decided that finally, they were going to actually remove ix?