In the poem "Stopping by Woods on a Snowy Evening," what do you think the "lovely, dark and deep woods" represent? Could it be death?

Since we're talking about poetry, the easy answer is of course it could.  Of course, because it's poetry it might not. 

A more literal reading is that our narrator is simply appreciating the beauty of the world around him on this, "the darkest evening of the year."  On this journey he is observing his surroundings, and the woods are simply an integral part of what he sees.  He draws us in to this winter scene and we are not in the least surprised by this description.

A more figurative reading is that the woods represent the narrator's intent to ride into the woods, never to come back.  If so, the death must be considered suicide rather than the natural ending of a life.  Finding certainty about this intent is probably not possible.

Because Frost is generally a symbolic writer, it's not surprising to have this kind of debate surrounding his work and specifically around phrases like this.  Part of the beauty of poetry is the opportunity for readers to explore and interpret--within reason--the language and imagery of the work.