Depreciate to what would be the question? If HTML5 were to depreciate then Facebook would go down quickly since that was the 1st major site to fully be made in HTML5.
Ok lets break it down logically
First a new programming language would have to come out and then all the major web browsers and phones would have to adopt it. That could take 10 years before its fully implemented.
Adobe flash support has been downgraded because of HTML5 yet people still make flash games and mobile games with adobe air. So even if HTML5 were done you still would be able to use it , the developer would just have to make a native exporter in that case.
Why HTML5 won't die and you don't have to worry!!!!
https://www.w3.org/ Is the group that controls which programming languages are going to die and which stay on the web. They are actively working on improvements to HTML5 going as far as to doing some of the grunt work themselves that they usually task to other developers to do which is a shock because they mainly just test and approve. Dude , don't worry HTML5 is in the Kings spot its not going to die anytime soon.