just kill it

I think PHP began as a simple preprocessing language. In C/C++, when you have an .h file you want to include into each and every .c file, you use the preprocessor directive "#include". What if you want the same thing for html? Say, have all pages the same header or footer? That's right, put "include" or "require" statement inside of your .html, rename it to have the .php extension - and you're done. That's the actual originating use of PHP, I presume. Of course it continued from then, but I think it never really evolved into an actual programming language -- rather than that, it stated the preprocessing one.

So basically, when you have a lot of html and only need simple structuring (e.g. make them use a single header or footer), you use PHP. If you're doing something much more complex, you'd probably be better with some other language. Therefore I think php have its niche and it isn't going anywhere.