Naxxramas achievement rewards that were removed with the launch of Ulduar in original Wrath of the Lich King will remainĀ available throughout Wrath Classic.

(Source)

As we approach Wrath Classic 3.4.1 and the release of Ulduar, we want to make sure all players know that the Glory of the Raider Black Proto-Drake, Plagued Proto-Drake, the Immortal title, and the Undying title will remain available to be earned throughout Wrath Classic.

Good luck earning these rewards in the months to come!