From what I've read, there is a lot of predicting going on regarding the "complete disruption" of the Internet infrastructure given the vast numbers of low-level attacks and vulnerabilities that have been discovered. One article even predicted an "eBomb" as quoted below:
There is a reason this is unlikely in the general Internet at large. An attack against the Internet infrastructure that "brings down the Internet" simply doesn't make anyone any money, in any practical way. While it may be beneficial to DDoS a competitor or wreak this type of havok for other reasons, they all eventually break down to finance. Someone, somewhere, made money on that attack. Denial of Services (DDoS) on a large scale simply isn't fruitful.
David Maynor, CTO with Errata Security, says '09 could be the year when the first large-scale and widespread attack occurs on the Internet's infrastructure. "I think with the [hacking] work being done on Cisco and routing gear in general we'll see the first wide-scale 'e-bomb' that will break peering between ISPs and make large portions of the Internet unreachable," Maynor says.
Most likely it will be a denial-of-service attack, he says, that will "break" sections of the Net.
If the chronology of attacks over the past year, or further, should teach us anything it's that everything is based on someone making money in the end. Money drives hacking as much as it drives prostitution, illegal gambling, or other illegal activities so while it's natural to think that the culmination of vulnerabilities will eventually lead to an attack that will completely shut down all Internet communication and disrupt service for days or weeks... that's just not likely.
That sort of attack may be be possible, but in a slightly different form. A disruptive attack may very well be coming against things like governments or internal critical infrastructures (such as SCADA systems?) This was already demonstrated once in a 2007 attack against Estonia. I can only speculate what kinds of attacks may be cooking in the dark corners of the minds of malicious individuals which could potentially disrupt governments, critical infrastructures, or other systems to cause chaos - but chaos even has a goal.
While the disruptive attack may very well be on the horizon for some portion of the Internet infrastructure... I personally feel it's very unlikely it'll be against the whole of the Internet ... without targeting some entity in particular... and I'm willing to bet that the end-game will involve making money somehow.