Both Rot Wolf and Abattoir Ghoul have triggered abilities that trigger when a creature that has been dealt damage by them goes to the graveyard. These abilities are ‘normal’ triggered abilities that will trigger when the trigger condition occurs, but only if these creatures are in play when it happens. These abilities are not delayed triggered abilities that wait around for the trigger condition to be met.

For example, let;s assume that an attacking Abattoir Ghoul is blocked by a Fortress Crab. When combat damage is dealt, neither of these creatures will go to the graveyard. If later in the second main phase, that Crab is targeted by Brimstone Volley and goes to the graveyard, the ability of the Abattoir Ghoul will trigger at this point. However, if the Abattoir Ghoul were to leave play before the Brimstone Volley resolves, the Ghoul’s ability cannot trigger.