With #250 Kubert was no longer writer or editor. Joe Orlando became editor. He had Gerry Conway & Jose Luis Garcia Lopez adapt ERB's Tarzan the Untamed. The story concluded in #256 with Denny O'Neil writing 255-256. Unfortunately Lopez' work was muddied by inks from the Redondo Studios & Rudy Florese.
#257-258 had Kubert reprints & DC's Tarzan was over.
ERB's estate wanted more Tarzan on the stands but Gold Key declined so ERB went to DC. DC did all the estate asked except for Kubert on art. ERB wanted a Russ Manning art style. Sales were good but not as good as ERB expected so they went to Marvel. They saw the success Marvel had adapting REH's Conan.
So Marvel put Roy Thomas & John Buscema on Tarzan hoping they could do as well as they had done on Conan. Thomas did stories similar to Kubert but even longer arcs. He left writing & editing Marvel's Tarzan with #14 after having issues with ERB's estate. John Buscema left with #18. David Kraft & later Bill Mantlo wrote #15-29 with Sal Buscema doing art on #19-29. Then Tarzan went into limbo until Malibu did Tarzan in 1992 & Dark Horse got the rights in 1996.