Both sides of Instigator Gang / Wildblood Pack have static abilities that give either a +1/+0 or +3/+0 bonus to attacking creatures controlled by the controller of this permanent. This bonus is applied as soon as a creature controlled by this player becomes an attacking creature and lasts until the combat phase ends or the Instigator Gang / Wolfblood Pack leaves play. If the Instigator Gang / Wolfblood Pack were to leave play before combat damage is assigned and dealt, then other attacking creatures will not have the boost when they deal damage.
For example, if a Wildblood Pack and a Crossway Vampire were to attack, the Wildblood Pack would be an 8/5 creature and the Crossway Vampire would be a 6/2. If the Wildblood Pack were to be destroyed by Rebuke before the combat damage step, then the +3/+0 bonus to the Crossway Vampire would end and the Vampire would only deal three points of combat damage.