I think you should focus more on the concept of OOP itself rather than languages that have OOP features. Way back in the day (I am actually a pretty young person myself but I feel old saying that, lol), I learned OOP while programming Perl (which by the way sucks compared to learning OOP while programming PHP). Eventually I moved over to PHP and easily caught on to its OOP features because I already knew the basic concepts. Anyway, no I do not think PHP is dying by any means. It has become a very popular web development language, regardless if people are using OOP or not in their PHP code.

OOP is never going to be the only way to go for software development in general. There are many other paradigms of software development such as procedural and component-based design, which will always compete with OOP one way or another. In my humble opinion, I think it would be very beneficial for you to learn OOP. So if PHP all of the sudden dies one day and some other language becomes popular, then the new language will most likely have OOP features as well. And since you already know the basics at that point, it will be very easy to pick up a new OOP programming language.