he's had injury problems for a long time. In 2008, he did run 43.xx after the coaching switch, but that switch was clearly the beginning of the end and allowed Merritt to beat him that year in the Olympics by a second. He had run 43.45 in 2007 to win Outdoor World gold and had he kept Clyde then, he might have gotten the world record the next year as Michael Johnson had been predicting. But let's look at this ridiculous comparison:
5x world's fastest time of the year.
3 Olympic Gold Medals (400--2004, 2x4x400)
1 Olympic Silver (400, 2008
2 World Outdoor 400m Gold Medals, 2005, 2007 (both sub 44)
1 World Outdoor 400m Silver (2009)
3x World Outdoor 4x400m Gold, 2005, 2007, 2009
That's 8 World or Olympic Gold Medals and he's #3 all-time in the 400m lists, behind MJ and Butch (who has a doping violation). No comparison to Webb, who never had any championship success and was further back on the lists as well.
By age, there's no reason he can't come back but 400m runners have not tended to have a long reign, with a few exceptions, and he has to overcome the injury history and throw down a sub 45 before the believers return. This was not auspicious but the 200m showed that he was in better shape.