Because of its removal from the vendor, many people thought that it wasn't going to appear when 3.0.8 goes live. Many folks have sent us tips via our tip line saying as much, and the official forums have multiple speculation posts on the subject.
However it appears that the removal was accidental and that by all indications Titanguard will be showing up in the live version. Maaven, the Blizzard blue poster over in the PTR forums, tells us all: "We'll investigate." Since they have been rather forthcoming lately as to the removal of PTR items (see the information about Death Knight tanking weapons), we're taking this to mean it's just a temporary issue.
"Don't Panic" tanks! That sexy 75 stamina will be yours soon enough.