Will Sass replace CSS in a few years?

SASS won't ever replace CSS. CSS is the standard developed by the W3C, and the one browser makers follow (and sometimes advance) when building their browsers' rendering engines.

However, SASS and other CSS pre-compilers like LESS and Stylus are making an impact on how people view the evolution of CSS. For example, there's a W3C working draft to include variables in CSS: http://dev.w3.org/csswg/css-variables/ These would act similarly to variables in SASS. However, other SASS features like mixins may never be included in the CSS specification.

SASS is a great tool to make it easier for us to generate the CSS that browsers use to format pages. It's better not to make web browsers do a lot of extra work -- like compiling CSS -- everytime they load a stylesheet. Pre-compilers are great, because we can write simpler, more modular CSS, and have our computers run through the necessary steps to generate pure CSS for browsers.

I suppose I should rephrase the question to more closely articulate my original intent. Do you think that CSS will fully integrate the features and concepts of Sass, LESS, etc... into CSS itself? It seems from your previous response, that it is already happening...