It's not about the term "HTML5" - its about the technology behind this.
And obviously canvas won't get lost some time soon. Actually the opposite is going to happen, canvas will be stuffed with more and more features as the standard grows.
You cannot really compare HTML5/Javascript driven game engines to anything Serverside like PHP. PHP is meant to do something entirely different.
Node Webkit does just fine, why don't you just try it and go see for yourself? There is acutally no real downside on this.