In JEP-60: Pubslish-Subscribe subscriptions are always persistent. That means that if the server/service goes down when it is restarted again subscriptions will be there. PubSub also specifies a concept called “leasing” where subscriptions can expire in a certain date. Anyway, subscriptions should be explicitly deleted by the subscriber or any node owner. And the expiration date (if any and if supported by the pubsub service) can also be configured by the subscriber.
PubSub in XMPP is meant to be used by XMPP clients (i.e. XMPP entities). That means that XMPP clients should also support PubSub (JEP-60) to be able to use the pubsub service hosted by the server. It is also possible to add “adapters” to the pubsub service where the adapter could let you integrate pubsub with any other type of application (e.g. email system, nntp, HTTP, etc.). Therefore, if you are looking for a solution that will let you just publish an item to a node by submitting an HTTP request using Plain Old XML (POX) you may use pubsub and you will also need to write an HTTP adapter. The HTTP/POX adapter would be a servlet that is added to the servlet container (e.g. jetty, tomcat, websphere, etc.) that parses the POX and interacts with the pubsub service. The HTTP adapter can also let users subscribe to nodes or whatever you need.
BTW, pubsub support will be released in Wildfire 2.6.0 that is coming out April 6th.