Usually the exact opposite thing happens, many users leave the threads open and then users "reopen" that thread after 4 or 5 years of inactivity to post their own question which may be similar to the original question.Other users can have valuable information to share even after the original poster thinks that the problem is solved.
Yes, that has to be accepted, if a close-my-thread feature exists. I don't think, that it's major problem. I remember a few cases, when I took part in discussion and found the thread closed overhasty, e.g. with a wrong solution, that has been gladly accepted by the original poster. On the other hand, nobody can correct all wrong or misleading solutions posted at edaboard.I guess there will be cases that a thread will remain closed with a wrong solution even after the OP is notified about the wrong solution.