If you've gone ahead and installed the Windows 8.1 and Windows Server 2012 Update (KB2919355), you might find that uninstall IIS can't be uninstalled. And, when you try to uninstall it, IIS will just roll back and stop functioning completely.
Not everything is easy to test during the Microsoft QA part of the patch release process, I guess. And, of course, we're finding that to be true more and more. But, really who uninstalls IIS? Customers.
If you're a Microsoft customer that fits this scenario, Microsoft has made a patch available that must be applied prior to attempting to uninstall IIS. There's no mention of what to do if you've already gone through this scenario and IIS has stopped working – just that the patch needs to be applied before attempting to uninstall IIS.