P.T. is no longer listed on the PlayStation Store following Konami's cancellation of Silent Hills, the Kojima Productions game that the "playable teaser" was teasing. But Polygon can confirm that as long as you added the free demo to your PlayStation Network account before Konami took it down today, you can still re-download it.
We originally "bought" and installed P.T. on April 28, two days before Konami delisted the game. This afternoon, we deleted the 1.37 GB demo from our PS4 hard drive. When we did so, the system gave us the usual notice it displays when you delete a downloaded item: "This application will be deleted. If you have a license for this application, you can download it again from [Library]."
Neither Konami nor Sony would comment prior to today's delisting whether that was actually true in the case of P.T. — whether people would indeed be able to re-download the demo. Thankfully for fans and preservationists, they can.
Immediately after deleting P.T., we went into our PS4's Library. P.T. was still listed there, and we were able to access the game page through the Library and start downloading it once again. After it installed, we started playing, and woke up in a small, dark room inhabited by nothing except a cockroach.
Konami's website for P.T. currently displays the message, "P.T. is no longer available for download, we appreciate any previous support of the game." Hopefully, you got it earlier and won't have to resort to eBay. If you weren't able to download P.T. before Konami took it down from the PlayStation Store, you can watch our Overview below to get a taste of the experience.