Bran wasn't nearly as affectionate as Gabby was, especially not with strangers; so after she'd said her goodbye or whatever it was he simply offered the man a polite nod. He seemed alright, level-headed and sensible at least, which was admirable. It was very unlikely that he'd ever see him again - he'd probably never see any of them, for that matter. "Thanks. Good luck with whatever you do, too." It was honest, albeit a little awkwardly stated.
He was actually shocked into silence when Gabby informed him that he was going with her. "I am?" It was hard to process the concept that she actually wanted him with her. Then, of course, he had to decide whether or not he wanted to go with her in the first place. Traveling alone was something he was used to, and he wasn't sure how being with another person would work out.
Then again... this was his chance. Erik would have refused and gone on his own, but Bran didn't have to do the same. He wasn't the same, and now that Bellum was gone there was nothing keeping him tied to a specific fate. He didn't have to let his story end like Erik's had. It couldn't hurt to give it a shot, right? "You don't have to demand anything," he said finally. "I'll come with you."