Hi,
The lifespan of IE 11 is tied to the lifecycle of the underlying Windows operating system. IE 11 is "the last version of Internet Explorer," according to a Microsoft FAQ document. IE 11 ships on Windows 10, so if a version of Windows 10 is still supported, presumably IE 11 is supported, too.
So seems that you still could develop your application based on IE 11 for a couple of years.
Bests,
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