An update: Apparently Empathy has switched from using GConf as its
settings storage to GSettings and its corresponding dconf. On the first
start of Empathy after doing the dist-upgrade, the Empathy settings are
imported once from GConf into dconf, and then GConf is no longer used
for empathy. Likewise, I imagine that for new 10.10 installs, there
never will be a GConf empathy entry.
As such, you cannot use gconf-editor to change the autoaway setting.
Instead, you must install the package dconf-tools and use dconf-editor,
which works very much like gconf-editor.