Kicking afk players don't need voting (i wonder how to vote, whether there are more players afk). After several minutes of inactivity, the game automatically flags you as AFK.
Leader should have button to initiate kicking procedure. All flagged players will receive warning a message box with information about kicking. Player will have 2 minutes to respond by pressing button in this window. Showing the message box can be also followed by appropriate sound notification.
Responding to the message removes AFK flag, so leader cannot repeat this until player becomes AFK again.
Not responding after 2 minutes will cause automatic recall from the quest, but not kick from the party. Others can use party chat for later communication with the kicked player.
Using this feature should have a cost. I suggest to pay by removing the group bonus XP for "reenter" (and rename this bonus to "re-enter and no kicking"). Kicked player may want to reenter to the quest later and it will also pay -20% XP for this (but this will not affect group "reenter" bonus, because it has been already paid).
(I hope, that this is understandable - sorry for my bad english)