The answer to this question is correct and should really be accepted, but I don't know if the user will return to do it.
Is it possible to mark an answer as accepted on their behalf?
As the answerer of the question in question, let me say:
Accepting answers is completely optional.
The question owner is not required to accept an answer to their question. We view accepting an answer as a simple social convention, a little informal “thank you” between the asker and answerer, a virtual tip o’ the hat to that person whose response, as the question owner, you personally found the most helpful.
That doesn’t mean the community will agree with your choice. But as the question owner, it is your choice to make.
The default sort order is “votes” for a reason. Normally, the best answer will automatically float to the top through community voting. This is important because we expect a lot of our question askers to be drive-bys, programmers who ask a single question, get the answer they need (or don’t), and are never seen again. This is intentional and by design.
Basically, voting is extremely important. Accepting answer is great, but we shouldn't be pushing users to do it if they're not ready. Users who accept too early potentially discourage other answerers. Of course, in this case I'm 100% sure that any answer not a duplicate of mine would be wrong; but the other points stand.
To address Raven's comment below: As long as at least one answer has a positive score, the question won't be bumped as unanswered; so that's not a concern.