当你听到某人要走了，你可以用以下句子来表达这个意思：

He is leaving.
He is on his way out.
He is departing.
He is on his way.

这些句子的来源都是源于英语中动词 "leave" 的不同形式，"leave" 本身的意思是 "离开，离去"。

例句：

I heard that he is leaving the company. (我听说他要离开这家公司了。)
He told me that he is on his way out. (他告诉我他要走了。)
I saw him departing from the airport. (我看到他从机场出发了。)
He said he is on his way to the meeting. (他说他要去开会了。)