My paper is accepted for a presentation in a conference; but I can not attend. Now what?
You'd have to ask the conference organization. You should try to get somebody to present the work for you, or (just out of courtesy) tell them it won't be presented (so they can schedule talks correctly).

What will happen is up to the conference. Some I've attended just did not publish papers which weren't presented, others did publish in their proceedings regardless (you had to pay any attendance fees, at the very least). What happens with "selected papers" also varies, one conference I went to selected papers only among those presented, including in their selection the presentation and questions and answers, asking selected authors for a revision based on the above.