If I understand the problem you are experiencing, what has happened is that several hundred contiguously adjacent nozzles on the green channel only, have stopped firing. I believe that the probability of an ink clog developing overnight, which affects this many adjacent nozzles, but nothing else on the head, is essentially zero.
If that is the case, it seems that there are two possible causes: physical damage to a portion of the print head, or a manufacturing defect.
Physical damage is almost always due to a head strike, and would affect the ink channel at one of the two outboard edges of the head. I do not believe that the green channel is one of the two outboard channels, and in any event, your problem description does not mention a head strike.
That leaves us with a manufacturing defect. I can think of several manufacturing defects which would manifest themselves only after a period of several months, and which could produce the symptoms you are experiencing. For example, that section of the nozzle assembly may have come detached from the main print head body, due to an adhesive failure. Or that group of nozzles could fail to fire due to a cold solder junction failure. Or ... the list goes on. I do not know much about the inside of an Epson print head, but your problem description makes it clear that the problem is almost certainly a manufacturing defect.
An ethical company would fix their manufacturing defects, and apologize for the inconvenience they caused.
If we search this Luminous Landscape forum, it is easy to find a very large number of complaints by Epson customers that their 7900/9900 printers have clear manufacturing defects, but that Seiko Epson has adamantly refused to address them. There are also reports of outstanding Epson service, but these are in the minority. While the sampling method is less than unbiased, I get the impression that Seiko Epson is a company that doesn't care much about customer service at the top - in Japan. There some terrific people in Epson who buck the corporate culture, and provide good service anyway, but it's not the Epson way.
By comparison, if we do a similar search on Canon large-format printers, we see a very different distribution - the majority of reports are positive.
My own take on Epson's rise to prominence, is that they entered the market with a technically superior product. Since large-format printers are typically interested in having the best possible prints, Epson quickly came to dominate the large-format market. Epson was able to ignore customer service without major consequences. My bet is that if you were to ask any member of the Epson board about customer service, you'd get an answer something like "We have a dominant market position, so we must be doing something right".
I'm personally interested in what makes companies succeed, and what makes companies fail. I think I see an analogy here. In the pre-press market, a product called Quark Express used to be dominant. Like Epson, they had a product which was technically superior. But Quark's customer service was notoriously horrible.
This went on for years, until another player entered the market. Adobe's InDesign wasn't technically superior to Quark Express, but Quark's customers made the unwieldy switch in droves. There are still a few people using Quark Express, but when I talk to them, they generally say that they are planning to make the switch to InDesign. Quark has gone through some major corporate restructuring, but the really odd thing is that I'm told that their customer service is still horrible. My take is that looking down on customers became so much a part of the Quark culture, that it was impossible for them to change. Now it's too late for them.
Today, people remember the time that they used Quark as "the bad old days". My guess is that Epson is a lot like Quark - that they did well when they had a clearly superior product, but that the company has never learned how to create and maintain satisfied customers. I could be wrong - and since I just bought an Epson 9900, I sure hope that I'm wrong, but I wouldn't be surprised to see a comment on the Luminous Landscape forum in ten years from now, along the lines of "do you remember the bad old days, when we all used Epson printers, and just had to live with their bad service?".
