It still exists. [1] Unfortunately its the same and looks out of place.
[1] http://www.superb.info/review-screenshots-os-x-yosemite/
It's disabled by default but can be turned on in System Preferences
i clicked the dashboard icon in launchpad and it got enabled and it looks exactly the same as mavericks
From what I can tell, Apple doesn't usually announce when they get rid of something. It just kind of fades out gradually and disappears one day (remember Sherlock?). Apple hasn't talked about the dashboard in quite a while.
It appears that Apple is adding widgets to the notifications bar in both iOS and OS X. Given that the two OSes are converging, and there is no iOS analog for the Dashboard, I'm guessing that the Dashboard is going away.