Buckley retired from the day to day operations of NR back in 1990. I would assume that decision was Lowry and/or Goldberg’s.
As Editor in Chief, which he handed to O’Sullivan.
But he retained his role as Chairman of the magazine, and was the ultimate decision-making authority until 1999 or 2000.
“As Peter Brimelow has related, much of the subsequent purges in the 90s centered around the then-burgeoning debate on immigration, and more specifically, the fact that Buckleys hand-picked replacement as editor, John OSullivan, had brought in NR writers seriously interested in the national question, Brimelow and Steve Sailer among them. With OSulliavan, NR was on the cutting edge for perhaps the last time in its history, publishing in 1992 Brimelows extensive 14,000-word call to Rethink Immigration.
Within five years, OSullivan was gone, as Buckley and his second attempt at an intellectual heir, Rich Lowry, moved the magazine in a direction that made it not only more palatable with the Wall Street Journal-set but the neconons, then close to being regnant within the conservative movement. “
http://takimag.com/article/national_review_purges_buckley/print#axzz4AH1RTqGz