I have a list of events that I hope to attend this year. Without ISPCON, will HostingCon become the replacement event? I doubt it. New owners this year moved it to DC in August. Snooze. (Didn't ISPCON go there to die?)
FISPA should certainly take this as an opportunity to pick up the fragments, but to do that they will need to do some out-reach, advertise, and plan ahead.
Why did it fail? Content wasn't always that appealing to the masses. Key Vendors didn't support it. Most importantly, the industry is very fragmented - DSL, wireless, hosting, MSP, etc. but also there are just too many shows (WINOG, NANOG, MUMS, Animal Farm, FISPA, HostingCon, MSPCON, etc.).
Remember that many shows, including the MSP Alliance show in Vegas in the fall of 2008 also had a poor showing (less than 200 folks like ISPCON in San Jose). Even the agent show, Channel Partners, is dipping. The economy is certainly playing into that, but ten if there isn't any value to the show other than drinking and networking will people really spend the money? (In my case, it's more about the time. I want an ROI on the time.)
If you are still looking to gather, maybe it's time for the ISPCamp - the Unconference - basically ISP-CEO extended for the day with attendees sharing, teaching and learning.