"Perhaps," there was no promise though. He couldn't be sure that Thomas would ever be ready to come out again. Erebus was not at all against holding the mortal down until he was gone completely if that was what it took. He did not hold sympathy for the mortals in that position. They were gods, they were meant to rule.
He continued to lovingly stroke her hair and then he dipped down and kissed her forehead like a father might.