Perhaps this really isn't so much a question of the actual city location and their 'potential' golf fans being able to sustain a tournament, but more a matter of how "the Tour" markets and manages itself going forward. If they can't draw a crowd in Chicago, well I don't see it as a lack of fan interest in golf, I see it as a lack of fan interest in "Tour Golf" as a brand.
As for the sponsors stepping up, and the right venue being picked for the tournament, well that is obviously going to be completely dependant on the way the economy unwinds further worse - or starts to recover. Watching a few of Arnie's comments last week, I think possibly the older players and those that have memories of golf pre-70s, might have some inkling of what is coming and what needs to be done by players as their responsibility to promote and work hard for the tour's health. But, I tend to think that the active younger players have no clue, and no motivation (yet) to really dig in and work very hard on their own individual efforts and assumed responsibility to promote all that they can manage to attempt to maintain their sports relavance in comparison to the public's perceptions of the merits of the sport of golf and need for diversion of a stunned and economically depressed population.
I think that the current perception of those that follow golf may be that "Tour Golf" is purse oriented. But a significant number of people only get charged up when the sport is 'competitive' oriented, with the example of the competition of the Ryder cup (non-purse in theory) capturing the most enthusiasm. If the tour can't keep the competition interest higher, with interesting venues and formats, I think they are in for a real and prolonged slide.
The other thing about a venue, like the question of survivability of Milwaukee's toon-a-mint is the atmosphere of the venue in its associated or ancillary activities and image. As I understand it, the Milwaukee stop for the players and more importantly their supporting cast of family and caddies and their caddies families has been a venue where they say the atmosphere is something of a mid-season picnic or reunione and there they let their hair down a bit. Brown Deer Park is a wonderful place for that. And, Milwaukee is a great city for that.