As a Musical Winds Down, the Writing's on the Wall.

At the lime-green wall, soon to be whitewashed, all the elements are there for poignant remembrances: a curtain scheduled to come down, forever; a creative genius who dies young, before his dreams come to life; a show about an exotic dancer who dies young and musically and slowly; and a doorway where the fans, more devoted than most, wait longer than usual, before and after each show. Add a felt-tipped pen or two, and the tributes are spreading on the wall of the Nederlander Theater, where ''Rent,'' one of the longest-running musicals on Broadway, is approaching its final act, with the closing date set for Sept. 7. [ABSTRACT FROM PUBLISHER]