John Lightfoot on Luke 9:31

[They spake of his decease.] The French and Italian translation do render this word decease too loosely. And I wish the English have not done it too narrowly; They spake of his decease. It were better, They spake of his departure. For the ascent of Christ into heaven was his exodus, as well as his death: nay, I may say more, if, at least, in the word exodus there be any allusion to the Israelites' going out of Egypt. For that was in victory and triumph, as also the ascent of Christ into heaven was.

There is no question but they did indeed discourse with him about his death and the manner of it; viz. his crucifixion: whereas, Moses and Elias themselves did depart without any pain or anguish. But I should think, however, there is more contained in that word; and that the expression the time of his receiving up, verse 51, hath some reference to his departure...