Personally, I believe that Nintendo aren't stupid enough to end what is a founding father of the gaming community, Zelda was made in 1986 which is near enough when any form of gaming started. It earns Nintendo way to much money for them to decide to pull the plug on Zelda's reign either, it's been doing so for 24 years, I don't think there are many other games series that have outlived that impressive feat, well besides games like Mario which have been striding strong for nearly 30.
I think the time that Nintendo will finish and bury the Zelda series (and even then it may not be forever) is when it's sales start to drop but while it's still a highly praised game series. I'd be disappointed if Nintendo got greedy and lost Zelda all of it's credit just for a little extra sash, especially considering they don't really need more money.