The title here is pretty straightforward. The address was published, but it's written like a speech, and speeches didn't go for punchy or catchy titles in the colonial era.

The main thing about the title is that it says up front what the purpose of the speech is: Washington wants to say goodbye. Yeah, he says a lot of other stuff, but he's saying it because he's stepping down and wants to pass on some advice before he goes. The fact that it's a goodbye speech is pretty crucial to the historical context.

Sometimes you don't need to find a good pun or a famous song lyric to create a clever title. Sometimes you just tell it like it is.