You can completely skip the siege machine part by just jumping down and to the right of each wall... youtube

Can I just say how awesomely hilarious the music choice for this video is? Hearing such epic, triumphant music while the fireteam runs away and completely avoids all combat is just great :)

You can completely skip the siege machine part by just jumping down and to the right of each wall... youtube

You don't get the chest, and you can't continue the raid. Best case scenario, you could grab the Exotic chest and SIVA fragment, but that's about it...