I don't remember the exact title, but it was part of a book of short stories, some of which I am also looking for. Its title was along the lines of 'My name is Devil', or 'I am Devil/Satan'.
Basically, a small Martian expedition travels to Earth after a great plague/war occurred, and the Martians don't find much. The Martians speak telepathically, too.
They leave one behind, who resides in a cave. He eventually finds a boy, and I think he has to touch the alien to speak with him, and the kid tells the Martian 'you're a devil'.
The kid and Martian eventually travel with a sled-toboggan type floating vehicle to an old man, who explains to the Martian how some kind of virus wiped them all out. They start a colony, where they find many different kinds of people.
I believe years pass, and the virus comes back. people leave, but the alien and I think the infected human go away for a few days, and both return, healthy again.
In the ending, the Alien goes to hibernation, that apparently happens to all of the Martians. A second Martian expedition arrives, and are surprised to see the thriving colony. The boy from the beginning meets them, tells them his name, and asks them when will the original Martian wake up.
The Martians go inside, and announce he will be waking up soon.