Complex sentence: Initially, his appointment was hailed as a major coup for the orchestra; however, after only one controversy-filled year, Wijnbergen left the orchestra in 1999, and it is unclear whether he resigned or was fired by the Philharmonic's board of directors.
Split into simpler sentences: Initially, his appointment was hailed as a major coup for the orchestra. Despite some successes, Wijnbergen left the orchestra in 1999 after only one controversy-filled year, and it is unclear whether he resigned or was fired by the Philharmonic's board of directors.