These quest will no longer be available in any present classic version or retail once Wrath is over

[Yehmi-trollbane]

Battle for Undercity got removed in Cata due to the fact that the scenario is completely bugged/broken. It still is in Wrath Classic because they didn’t bother to fix it. If you want to read more:
Battle for Undercity Issues - Updated 10/4 - WoW Classic / Wrath of the Lich King Classic Discussion - World of Warcraft Forums (blizzard.com)

@Aggrend-1483

We knew going into Wrath Classic that this event was fragile, and indeed, the Battle for Undercity breaking was a very common problem in 2008 at original Wrath launch. This event continued to be problematic for the entire history of Wrath of the Lich King until it was removed from the game in patch 4.0.3.