Perkun Wars optimal strategy

In the Perkun Wars there are three NPCs: Dorban, Pregor and Thragos. Dorban is a witcher, he is continuously hunting the vampire. Pregor and Thragos are humans - they are avoiding the vampire. You can attack the vampire whenever you see him, but it is the best idea to attack him when the NPCs are around.

There are two strategies: either you will hunt the vampire just like Dorban does (and thus you will mainly cooperate with Dorban) or you will wait with the humans till the vampire comes himself. The latter strategy is better - because the help of Pregor and Thragos is better than the help of Dorban. Very rarely you will be lucky enough to meet the vampire with all the three NPCs. This is your opportunity - attack him!