@ak2508 they arent violent criminals and even if they were, there's two things that could happen:
1) they knock him out but then when he wakes up, he has the confirmation that its the people Teiai is looking for so they'll have to abandon the van. Knowing how hard it was to find an untrackable van, they'll have a hard time finding a replacement vehicle.
2) they kill him but in that case they'd end up having both the cops and Teiai looking for them.
And thats only in the best scenario. If someone witnesses the murder or fight, the situation could get even more hairy. The best option really would be to lose Pestilence without giving him a confirmation of their identity, I guess they'll stick with that and even if Pestilence reaches them, then the worst case scenario is simply that they have to ditch the van right there and then, which is the same thing as if they attacked the guy (although an attack might give them more time to dump the van and escape with part of the cash, but then again there might be witnesses).