Complex sentence: O'Hanlon and Blanc both died in 1989 during production of the film, which was dedicated to both their memories and since no new episodes or any new spinoffs produced to continue from where the show left off, the film serves as the finale to the television series.
Split into simpler sentences: O'Hanlon and Blanc both died in 1989 during production of the film, which was dedicated to both their memories. Since there were no new episodes produced to continue from where the show left off, the film serves as the finale to the television series.