It could be smaller like this:

on 1:dialog:away:init:0: {
did -a $dname 3 %away.extension
did -a $dname 4 %away.msg
}
on 1:dialog:away:edit::{
if ($did == 3) { set %away.extension $did($dname,3) }
if ($did == 4) { set %away.msg $did($dname,4) }
}
on 1:dialog:away:sclick:: {
if ($did == 5) { afk %away.msg }
if ($did == 6) { back }
}

Good job :)