As a former Nortel exec, my opinion is that Roth set the company up for ruin.  He bet everything on optical success, and shortchanged wireless, enterprise, and all other businesses.  He bought smoke and mirrors optical startups, invested heavily, and refused to sell the optical components business to Corning for $$$ before the crash.  All the while he was collecting 10-100's millions in bonuses and stock options based on inflating Nortel stock price.  After the crash of 2000, he collected his severance and pension, banked all his bonuses, and left it to Dunn, Owens, and Zafirovski to try and save the company.  Only a very good exec could have saved Nortel, and none of these folks were much good, so the company failed.