"Afterwards" seems like a fairly easy title – it is, after all, only one word. But like most of Hardy's poetry, there's more to this deceptively simple title than meets the eye. The word "afterwards" is an adverb – it describes when something happens. So the title suggests the continual forward movement of time, since the poem takes place in the future, after some event that hasn't happened yet at the time it is being written.
But "after" what? What event does the poem refer to in the title? To the death of the speaker: the entire poem is a meditation on what will happen "afterwards" – after he dies. There's also a possible pun in the title – the poet wants to know how he'll be remembered as a writer. Will people remember his words? What will happen "after words"? There's a lot of weird ambiguity having to do with the passage of time all wrapped up in that deceptively simple title.