He expected me to answer with HTML5 which is technically a wrong answer because HTML5 is a standard and as a standard it won't replace anything. Once I finally understood what he meant with the question I said "New technologies specified and introduced with the new HTML5 standard are possibly going to replace parts (eg. audio and video) for which you had to use 3rd party plugins like Adobe Flash before but except for the Microsoft counterpart Silverlight, which definitely will never replace Flash, there is nothing that could completely replace Flash."