So from what I know the MOP CM guild achievement pet was removed, but I'm not sure when exactly it became non-purchasable. Was it pre-patch or WOD launch or when exactly.

I'm wondering then will Deathwatch Hatchling http://www.wowhead.com/item=114968/deathwatch-hatchling follow the same fate and become retired / impossible to buy from guild vendor after challenge mode removal in the upcoming patch.

Anyone has any info on this?

You can't cage them so there's no point stockpiling them to sell later, but probably it's a good idea to buy one for a collection ASAP just in case.

Came to my mind after some guy posted on my realm forums he's looking for a guild with this pet, I gave him my battletag yet he didn't bother to reply me for 3 days, so either he got it from somewhere else (hopefully) or people really believe they have all the time they want to still buy it and in that case I'm wondering if that's true or on Wednesday (I'm on EU servers) people are gonna get surprised the pet got removed from the guild vendor.