In fact, Sarah has no choice. Lester is the man who gives freedom, security, and care, unlike the loser Dan, and deep down her soul she perfectly understands that Lester is her future.
From chapter 16, Dan became the background in this story as an annoying fly and does not affect anything at all. You should always look at what they do, not what they say.
Dan will still be very lucky if he ends up homeless or in prison, at the hands of Sara and manipulated by Lester, and not at the hands of himself, although I don't know which is better. It's a dark story DS said….
That in real life and in stories there is a point of no return, so we have already passed this point. Dan is the past for Sarah, so he should not do it now.