It's tempting to snap back at Sam, to return to bickering, but Dean ultimately lets silence stretch between them instead. He doesn't want to give Sam leeway to keep questioning, and he could use some time to think.

As he drives, he can hear Sam murmuring in his sleep. Dean ignores it — doesn't try to wake him up, since some sleep, however fitful, it better than none. He needs Sam to heal up some more, to watch his back on stops so they can make it back to the only safe camp out there.

In those quiet moments, Dean thinks about how Sam is still alive. Because of the freaking devil — but alive nonetheless. As is typical for Dean, especially these days, he attempts to quell any potential emotional reaction to that — Sam's still here, and they have a job to do. That's that.

It's bad enough that Dean lost his tightly kept control once already.

After Sam speaks, Dean answers, without any hesitation. "It'll work."

It has to work. It's their only chance.

"Or it'll be the end."

And that will be that.