Nortel's ( NT) vice chairman and former CEO, John Roth, will bid adieu to the sputtering phone network-equipment maker this spring. The announcement came Thursday as Frank Dunn, former CFO, officially took the top job. Roth, along with nonexecutive director Lynton "Red" Wilson, had shared a special office of the chief executive with Dunn, who moved into the top spot in November after a prolonged search to find a new leader. Like most of its peers, Nortel stock has plunged over the past 18 months as the telecom business has gone into a nosedive; it closed down 9 cents Thursday at $5.07. After a 33-year career with Nortel, Roth will leave when his term as nonexecutive director ends in April. During Roth's tenure, Nortel famously exceeded rival Lucent ( LU) in sales, driven in large part by Roth's decision to focus the company on a new generation of fiber-optic technology. But it was also on Roth's watch that Nortel failed to predict the collapse of network-equipment demand, which subsequently forced the company to slash its staff by half to keep pace with plunging revenue flows. Investors left to ponder Roth's legacy also still question the executive's strategic judgment in pushing boldly into financing arrangements in the risky high-speed wireless Internet market known as third-generation, or 3G. But now Dunn's got the catbird seat all to himself, along with the second-guessing. Nortel watchers shall surely rise to the occasion.