Well, the mainstream support for vista ends in 2012. but that doesn't mean you still can buy the OS till then.
I think they will keep Vista around for businesses that want all their new PCs have the same OS and then at some time forklift all PCs to a new OS. but for the regular OEM and users they probably will stop selling it as soon as W7 becomes a success. I guess the market will phase it out on its own. the better is the enemy of the good.
I'm waiting to get W7 at work. We have XP and not having a pinnable taskbar sucks :-)
I'm afraid in 1 year they will switch us to Vista at work... I hope not. but next year they will switch us to Office 2007. Hello, why spend the same money on Office 2007 when you get Office 2010? Especially since everyone gets expensive mandatory training? So I really hope Vista will be killed just to prevent out IT department from ever buying it.