Complex sentence: Sinclair takes the rocket to save himself, but not before Cliff thumbs off the chewing gum patch; with the leaking fuel ignited by the exhaust flame, Sinclair dies crashing down upon the last four giant letters of the "Hollywoodland" sign.
Split into simpler sentences: Sinclair takes the rocket to save himself, but Cliff pulls off the chewing gum patch. In the explosion, Sinclair dies crashing into the last four giant letters of the "Hollywoodland" sign.