Quest ~ Messenger to Thrall ~
This quest has been removed as of patch 4.0.1

This was taken care of by the guide writers!

I'm currently leveling a Horde character through HFP. Nothing in the HFP guide was different to this point. I'll update this comment if I find anything else out of the ordinary.

After some research, it appears that no other quests can be completed for the Mag'har in HFP after the initial spirit-walker quest. That means the following QIDs are currently impossible to complete: 9438, 9441, 9442, 9447. I feel like there was one other quest, but I couldn't find it. With the removal of all these quests, I'm not sure if it's possible to complete the quest achievement for HFP without doing a few of the dungeon and PvP quests.

Lines 237, 264-270, 277-278, 387-390 in horde/60_63_Jame_Hellfire_Peninsula.lua are part of the removed quest line.

Thanks a ton for the detailed report!

This guide needs to be looked at in detail, as I'm not certain what follow-ups still exist or if they were completely removed. Anyone questing in Hellfire on the Horde side, this would be a big help!

According to wowhead, it looks like you can do the To Hellfire and Back achievement post-Cataclysm. You might have to do dang near all the quests in the zone, but it doesn't look like you need to do the dungeon or PvP ones. You might need to do Report to Zurai that gets handed in over in Zangarmarsh though. I've got a priest that's almost to HFP - I'll see if I can run her through the horde guide in the next week or two and keep tabs on what's good and not.