I don't think he should retire if he doesn't want to. Despite his head trauma. Besides he didn't look as bad as his last few fights. He looked okay in there. He can still beat other guys. Remember when Andre Arlovski kept getting slept. And everyone said he should retire. Then he went on a good run in the UFC.
Now regarding the head trauma we are in an age now where the technology to repair the brain is almost public. It already exists "behind the scenes". By the time Bigfoot is old, medicine would have advanced he'll be okay IMO. Besides the damage has already been done... Look at Overeem he has been slept more times, and is still a contender. It is a little different for the heavyweights.
Now if Bigfoot looked like complete dog shit, I too would have said retire. But he performed well in the first round. Roy Nelson sleeps most the guys he faces, so no shame in losing to him that way. And Bigfoot didn't even go completely out. So he showed he still has somewhat of a chin. This may not be a popular opinion, I know you guys care about his health. But what about his family? How else can he make that kind of money? If he can find something great. But if fighting is what he loves and what provides for him, then who am I to tell him what to do. His brain, his life...