... why did it stop? Did the end of Kirby coincide with McKenzie leaving the Prog?
David Bishop says he replaced McKenzie as Tharg on December 18th 1994
. The last full series of Luke Kirby ran six months later, so it seems safe to assume that was an example of Bishop/McManus running something that was already in the pipeline when they assumed the Planet Of The Apes
mask and overalls.
McKenzie's most recent post-mortem appearance in 2000ad was RAM Raiders
(1996), which seems like the definition of the stuffwefoundatthebackofacupboardthatthepublishersmadeusputinthecomic
mentioned in Thrillpower Overload
His awful Chopper series and the Brigand Doom with the vampire accountant show up around the six month mark too, but I don't think McKenzie was ever commissioned to write for the comic after he left, whatever the reasons for that departure were.