It was brought to my attention on WarcraftPets that the quest from Umi Rumplesnicker that trains eligible engineers the Tranquil Mechanical Yeti schematic, is no longer available (as of around patch 5.2). The quest, A Yeti of Your Own, was either removed or severed from the quest chain, and it's unknown if Blizzard intends on bringing it back in the future.
Fortunately, engineers that learned the recipe prior to the quest's disappearance can still craft the yeti. The pet can also drop from Blingtron's daily quest. It has quite a low droprate, but the pet is still obtainable.
Now that this pet can only be obtained as a drop or as a trade/purchase, I wonder if that will affect the pet's price on the Auction House. The recipe isn't exactly super rare or difficult to craft, though, and I'm sure many long-time players can craft the pet. I don't follow the AH trends very much, so I'm pretty clueless as to what will happen to the supply and demand.
I'm curious as to what exactly happened to the quest, and wonder if its disappearance was intentional or not. I'm not aware of any major changes in Winterspring or the quest chains located there pre or post Patch 5.2, so I can't think of anything that would cause this quest to go missing. If anyone has some insight on this, please share! I'd love to know. :)
Until more information surfaces, I'm currently leaning towards the point of view that its removal was ultimately intentional. With the implementation of Blingtron and his ability to drop all engineering pets, perhaps Blizzard decided to streamline the acquirability of the yeti and reduce the number of sources it can come from.
Even if it wasn't an intentional change, Blizzard might be ok with the way things currently are. The Tranquil Mechanical Yeti is still completely available, trading/buying from an engineer that can craft it or from Blingtron's daily, so it's possible that they see the original quest as unnecessary now.
Well, that's all speculation on my part. We'll see what happens in the future.