Not in a form we know PHP today. If large companies (like Facebook) uses it (HHVM) it will be forked and made better. It really just needs a talented team who can make it better but it won't be called PHP anymore. JavaScript is a trend but I don't think that will last either because the community gets more and more diverse, frameworks are released almost daily.
New languages. This is the key. Something new will come as always. In the beginning when PHP started, tech was evolving slowly. So it lasted a lot because it was the perfect time to start a programming language but nowadays it is way harder to keep up with the trending stuff. New languages like Go focus on making the language itself modern and the community good and exclusive.
I have a tip that the Apple-backed Swift will last longer than the languages we know today but that is just a personal tip.
Also if you look at the startup scene today, you won't really see startups written with PHP. If someone writes a codebase in PHP, he is considered oldschool in Silicon Valley and lame. And this generation will form the next 20 years if you think about it.
Conclusion: It will be around but mostly as a fork, not the base language