I wouldn't expect the 'group' to retaliate. Most of them are just victims after all. They've been victimized by their powers since the moment they discovered them, for the most part. And if Parkmen seeks vengeance I am sure he will end up doing something stupid and I 'aint lookin' forward to seeing that.
Considering Nate showed Mercy towards Peter and Claire, I assume mercy will be showed upon him for all of the borderline unacceptable stuffed he's deluded himself into pulling. In that case, I'm sure we will see that messed up family get away with loads of BS for seasons to come or until the show finally gets pulled.
Oh and I don't like the fact that the writers are letting something 'mystical' carry the plot yet again. Twice it was people from the 'future' and the 'affects of the future' that influenced and carried every decision of the main cast, and we see what sort of train wreck that was. Now Parkman is getting mysterious visions that not only DON'T HELP HIM AT ALL but create deus ex machina upon deus ex machina. His visions are the sole reason for convenient plot development but they have no rhyme or reason... I am beginning to hate this show.