The ending is wonderful if you give some thought to it.
I'll just get the Llewelyn issue out of the way first: yes, he's dead, and so is his wife. Anton checks his boots for blood after leaving her home.
As for the ending itself, you have to consider the film as a whole. It opens with Sheriff Bell's telling a story about a murderer who said he would kill again if released from prison over footage of the desolate Texas landscape. His point is that sometimes it seems futile to even try to stop evil; evil will always win out. It's why he's planning to retire from law enforcement.
During the action of the movie, Bell is trying to track down Anton, an amoral sociopath with no respect for the law. He kills who he wants. He's basically evil personified. And no matter how hard Bell tries, he can't stop Anton from killing.
And in the end, Anton has the money. Anton has killed Moss, his wife, Wells, and the man who hired him. Anton walks away. All of Bell's work was for naught.
And so, we end with Bell right where he started: telling a story. This time, it's about the dream he had about following his dead father on horseback. The story provides a bookend to complement the beginning; he has learned what his father once learned. The bad guys will eventually win, even if you dedicate your life to stopping them. And so, he has no choice but to follow his father into the sunset. To leave it behind and sit by the fire.
It's beautiful how they tie in the barren desert plains from the start of the film with the similarly bleak result. The landscape is, and will always be, desolate. Murderers will continue to murder, no matter how much you try to deter them with prison, the death penalty, what have you.
It's not a pick-me-up, but it's certainly a fantastic choice from an artistic viewpoint.
my mind. It's late, so this might not be as eloquent as it could be. But I've had this conversation before.