If he had killed Brock definitely, because Jesse is a character that has a soft side with kids, we see that through all seasons in Breaking Bad, remember when Andrea told him his brother is part of a "gang" ? Jesse almost began a war with Gus because he was against the use of kids for the meth distribution on streets, and when he realized those dealers murdered him, if it wasn't because Walter showed up, Jesse would've definitely killed them in revenge
