Chicago would be nowhere near as prosperous without Daley pere et fils.
Nice use of French, but I completely disagree with this assertion. By 1955 Chicago had already been America's second-most populous city for about 60 years (in fact, it was more populous than it is today). Cities that size
can fail (see: Detroit), but failure is far from being an overwhelming likelihood. I would say it's far more likely that, without Daley, the calcifying and corrupting effects of Chicago machine politics abate somewhat. Even if removing Daley does not affect the Chicago machine, we would still have to consider the possibility that other mayors would have proven to be just as competent at managing the city. For example, some people would say that OTL Harold Washington was Daley's equal.