I don't think they talked about anything on the way to Dayton. I don't think Dean attempted to communicate at all--or responded to others' attempts. Just one foot in front of the other to get to Mary and Jack, the others could keep up or not. I'm convinced that when he got Cas, Gabriel, and the civilian to the camp, he intended to turn right around and go after Sam alone.

But seeing both Mary and Jack, and a camp full of armed people, he reconsidered on the spot. I took the "We have to go back" as an invitation to Mary, if she wanted to come--perhaps she needed some closure. In any case, Dean was going back, anyone from camp who wanted to go with him, and Jack, if Jack would go, and Dean would apply a little pressure to get Jack to go, if he had to. Sam was Jack's, more than anybody was Jack's, and maybe, just maybe, Jack's mojo would be enough to bring Sam back. Not counting on it (but yeah, counting on it, a little bit).

Gabriel was useless, Cas was worse than useless he was deleterious, and frankly, I'm so pissed at Cas my headcanon Dean can't stand to look at him right now. So the "we" to me, read, Mary, if you want, and Jack, and anybody else but Cas.