Comment by berkes

Depends on how it is set up.

Many modern hosts run php in fcgi mode, where your app is a process that listens on some http port. And where the webserver is "just" a proxy and ssl termination. Shutting down the process is enough.

But traditionally, php was a module loaded into apache. Where apache not only handled ssl, http etc, but also compiled and ran php for you. With that setup, adding an html file, will keep the php runtime and app online.