Updates to Internet Explorer are tied to the version of the Windows operating system, as mentioned in this blog post. Quoted:
Internet Explorer is considered as a component of the operating system (OS) for which it was released. The support timelines for IE are inherited from the OS and its associated service packs. Basically, this means that the versions of Internet Explorer that shipped for a specific OS or service pack will be supported with the support lifecycle of the OS or service pack. Support for older versions of IE will not end unless we ship a replacement version of IE in a future OS service pack.
However, Windows Vista and Windows 7 have not been given an support end date. You may want to look out for any announcements from Microsoft ending support for any of these OSes, and upgrade accordingly.