The armies of the Vampire Counts are held together by the necromantic magic of their generals. It is their will that raises the legions of Undeath from the cold earth and summons unclean creatures from the wilds. Without this magical animus, the Undead fall lifeless to the ground and the creatures of the night return to the dark forests.
Source: Warhammer: The Old World Online Rules Index
The Death of a GeneralURL Copied!
Every Vampire Counts army is animated and driven onwards by the sorcery of its General. To represent this, the General of a Vampire Counts army must also be a Wizard (be they a Vampire, a Necromancer or a Strigoi Ghoul King). If your army includes only a single Wizard, that Wizard must be your General, even if they are not the character with the highest Leadership in your army.
Should your General be slain, the magical animus of the army starts to dissipate. As soon as your General is removed from play as a casualty, all friendly units with the Necromantic Undead special rule lose the Regeneration (X) special rule.
In addition, at the end of the phase in which your General was removed from play as a casualty, and during each of your Start of Turn sub-phases for the remainder of the game, all friendly units with the Necromantic Undead special rule that are currently on the battlefield must make a Leadership test. If this test is failed, the unit loses a number of Wounds equal to the amount by which it failed the test.
For example, your army's General is destroyed during your opponent's Shooting phase. At the end of that phase a unit of Skeleton Warriors (Ld 5) makes a Leadership test and rolls a 7 (failing the test by 2). That unit immediately loses two Wounds. During your next Start of Turn sub-phase, the same unit makes another Leadership test, this time rolling a 6, resulting in the loss of one Wound.