Whichever buffs Z would cast before initiating an ambush is not so important as the fact that, as V noted, Z took out the archer rather than the wizard as an opening gambit. This indicates that Z is weak against archers, unless the whole "dominate-the-kobold" ploy was an error.
Another unresolved issue is whether the LG in fact thinks V is lost to the party or made the reasonable assumption that the Order would retrieve their wizard from the Plane Of Torment. It seems likely Qarr didn't disclose to LG his little misdirection since being trusted is an important part of his "familiar" role. However, if you were a party with no arcane caster (other than possibly Elan) would you invest the time necessary to retrieve your beloved party member and Big Gun? If so, it is reasonable that Tarquin allowed for the possibility.... although it's also possible T figures that since he's so much smarter than everyone else around, the Order was too stupid to save V. We may see.