Facebook Graph Search a Google Search killer?
No, because Facebook Graph Search (FGS) goes only through the, well, social graph. In some cases it might refer people to some Bing results, but from what I’ve read so far that will be a comparably rare case.
Facebook wants people to stay on site, while Google (Search) — ultimately — wants people to leave the site as fast as possible with the best possible result waiting at the other end.
I think FGS has been hugely over-estimated today: most media seem to have understood that FGS is something like a real search-engine, where it is really just an improved way to finally find some information on Facebook itself. If Facebook really would want to build a web-wide search-engine, they would not have improved their partnership with Bing, right?
The ultimate goal?
To answer the other question: No, I don’t think it is the ultimate goal. Facebook is in the business of gathering data about their users to be able to target ads better and sells ad-slots at higher prices.
Google is in the business of gathering data about the web itself and analyzing those data in order to make people come back to their site because these people find what they want to find. (Obviously, Google also tries to gather data from other location, such as Google+, to also target ads better).
In general, you see, Facebook and Google have different business models even though they seem to be the same at the first look. That’s why Facebook will never try to build a comparable search-engine like the one Google operates.