Definitely, not only it may happen, it's
already happening!
Ideally, for MS, each Windows version should cease to exist as soon as the next is released, so people buy the newer and pay again for software they already have. Both Vista and 8 were failures, let's face it, most copies that were "sold" are in fact part of the
Windows Tax you pay when purchasing a new computer. On the contrary, XP and 7 were successful in their own right and merits.
MS would love to immediately kill both so all people buy whatever they begin to sell next, but the reality is that changing of stable systems is not so frequent, specially in businesses, so both may live for a looooong time, much longer that MS would like, and possibly longer than MS officially "supports" it, as it's the case right now with XP. I guess the same would happen to 7, unless 9 becomes really good and offers improvements, restores deleted functions and allows easy compatiblity with existing programs.
M$ has made it pretty clear it has no intention of extending Win 7. It won't even make a SP2.
Maybe MS doesn't plan to support it anymore, but if the OS continues to be used, the community will for sure provide help! Just look at the unofficial XP "SP4". And from MS point of view, that's equally damaging as providing support themselves, as the users will not buy the latest crapware they release.