This incorrect. While Gecko is not in its entirety going away, components of Gecko will be replaced with Servo's code.

Such is detailed at Servo's roadmap. https://github.com/servo/servo/wiki/Roadmap

Specficially:

>> Internally committed 2016 goals

>> Ship one Rust component in Firefox Nightly, riding the trains

>> Experiment with the uplift of a major piece of Servo into Gecko