**** THIS IS NOT A COMPLETE WALKTHROUGH. INFORMATION WITHIN IS FROM PERSONAL EXPERIENCE HAVING JUST COMPLETED THE QUEST/SCENARIO ****
Hope this will help you along until someone does a more clear cut and precise guide.
Broad overview of this quest as I did it:
First, you will fly Thunderwing Doomslayer and use smoke bombs to disable sentry totems. I didn't know exactly what I was trying to do, other than create a "path" for later on. I'm not sure if it lets you get to the next stage or not if you don't do a good job, or whether you only have one go at it before the next part begins. It's doesn't seem to matter match (as shown later in this post).
Next you will follow around [npc=69544] and disable some Zandalari with your Extra Action button. The ones you are to disable are marked, and its quite simple. (Note: If you lose your stealth it's probably because you lost [npc=69544] from not disabling a mark Zandalari and going on ahead. Find them again via backtracking, and if mobs are agro'd Taoshi puts down a purple smoke you can run in and restealth). Continue on, following Taoshi and disabling mobs that are marked. If you're not a Rogue, and never been one, you might get a kick out of this part. Pardon the pun. Taoshi will be putting bombs throughout the ship, if you're wondering what's going on.
And then... you will follow [npc=69544] down to [npc=69482] . He mostly does melee attacks with the occasional keg toss ability. He might have a Drunken Wanderer help him out which will melee you as well. [npc=69544] puts recuperate on you if you get lowish on health, but remain cautious. He's not all that easy if you have a low ilvl (460-470). If you do happen to die, don't release. [npc=69544] will finish him off and you will rez at the docks to continue on. If you release, you will be rezzed at the graveyard and will have to fly Thunderwing back to the ship from the graveyard and fight the Captain again.
And then... after you kill the Captain, [npc=69544] leaves you! Just kidding. But I had to go back out the way you came in getting to Captain's Halu'kal (i.e. (up the stairs). Then go North and jump off the ship (this is the way I went, you might be able to stay in the room you killed the Captain in and theres an exit down there. I didn't look, I just ran back upstairs and jumped off the ship.) [npc=69544] will be waiting, stealthed, on the docks for you. After killing the Captain, there is an exit from that room. Plain as sight! It takes you right out to the docks to continue on the scenario.
Navigate up to the skull on map to [npc=69483]. You might have to walk through some sentry totem areas...i walked through them quickly and nothing happened. So, avoid mobs. Be careful. Again this is not a walkthrough. I'm sure you're not suppose to walk in the cyan circles.... this is why you threw down the smoke bombs in the beginning; to clear a path.
And then....kill the Gatekeeper... loot the orb. Open the gate. You're done!