I normally create a comment about it on the question concerned. If the user acts on it, I can always remove the comment or issue a thank you. Most users will react fine to such comments; most just don't know or forgot about the question.
Others don't any may leave stackoverflow. This is fine by me: less persons that don't give a shit about stackoverflow community. It's better for them to leave than to have the equivalent of a StackOverflow troll.
For me it is not so much that a question has to be accepted for the points. It's more that they keep drawing attention even though valid answers have been accepted. This is especially true for less used tags (almost all my points are on [encryption], highest upvote = 5 at the time of writing) where questions generally get less upvotes, stay longer in the "newest" queue and are therefore much trickier to filter out.