Elijah never died, and therefore, he can return. The prophesies in Malachi, Sirach, and other parts of Jewish thought, proclaim that Elijah will return. Malachi says that the Law and Moses must be remembered, but that Elijah will be directly encountered.
In the story of the widow, we should see Advent. We have a humble and intimate story. God working through small things – birds and the small gifts of a poor widow. The characters are mundane, and the location is marginal. Small people doing small things in unlikely places. And through them, God invades enemy-occupied territory to bring dead things back to life.