Deathcharger (Baron Rivendare's) mount not going away.

[tacdriver]

New thread MMO champion blue tracker states: "Deathcharger's Reins will retain its current drop rate, but will be moved from Baron Rivendare to Lord Aurius Rivendare when that transition occurs".

Other noteable changes:

Swift Zulian Tiger
Zul'Gurub is changing from a raid to a leveling zone in 4.0.3, and this mount will no longer be obtainable.

Swift Razzashi Raptor
This mount will also no longer be obtainable after the change to Zul'Gurub.

Razzashi Hatchling
With the change to Zul'Gurub this non-combat pet will no longer be obtainable.

Tome of Polymorph: Turtle
This tome will continue to be available through other means.

Crusader's White/Black Warhorse and Swift Alliance Steed/Swift Horde Wolf
As the attempt-based tribute system is being removed from Heroic Trial of the Crusader, the Argent Crusade Tribute Chest will no longer spawn, and these mounts will no longer be obtainable

Reins of the Blue Drake
This mount will once again be available from defeating 10-player Malygos without needing to use the Dungeon Finder. The Reins of the Azure Drake will only be available on 25-player Malygos.

Mimiron's Head
This mount will change to be a very low drop chance when defeating 25-player Yogg'Saron with no Keepers assisting you

Invincible
This mount will change to be a very low drop chance when defeating Heroic 25-player Lich King