Person who writes PHP for a living here. The argument that "PHP is dying" is one I hear from one of my clients who pays me to write PHP all day, and even more ironically, his proposed replacement would be done in Python, which is even older than PHP.
PHP is still used at Wikipedia and every site on the web that runs WordPress. It's not going anywhere in the near future and pretty much all of the hard problems have been solved with it. It doesn't have the flash and hype of newer languages, but there's no web-related problem it can't solve incredibly efficiently.
If it comes to losing the XenForo license, rather than rewriting the forums with Laravel, have you considered
Vanilla? It's the closest in feature parity to Xen from what I've seen and is available with a real OSS license (though a lot of the documentation tries to push you towards the hosted product).