The 3 sleepers can be found again in the Broken Valley village, at the back IIRC near the talking cart. I don't recall running into the guy from the troll trap again.
Supposedly the only person to survive the Temple of Doom was the leader of the bandits, but defeating him wouldn't necessarily make you the new leader (through it probably would if the bandits were not destined to get wiped out, which can happen before you enter the temple, so there wouldn't be much left to lead in that case).
You can go through with the robbery or not, and it will not effect other quests or influence other NPCs. Actually, after helping the traders I went back to the bandit camp hoping to be able to report on the situation, but didn't get the reaction I was hoping for (one of the responses was quite amusing, though).
For the Hellgate orb thingy, you can get a demon's claw from the last opponent, one of 2 or 3 ways to solve the 'Greater Hunter' quest.
I saved and tried the quest with Lovis' soul stone both ways. There is quit a funny dialog option if you decide to help the ghosts, but the reward is worse and you don't get the second chest in the throne room (which in D2:ED contains a random legendary quality piece of equipment).
You can kill the champion, but the quest reward is worse, the promised reward from the Red Hammer chief was a lie, and he will attack you anyway. Again, I had saved before entering the cave, so tried the quest both ways. AFAIK there are no consequences for killing the champion; nobody noticed right away, anyway.
After getting a couple skill points from the blind philosopher he isn't involved in anything else.
Which quest failed when you helped Saul? The quest from the slayer will fail if you help Saul escape, but if you picked Kenneth as your trainer that quest should pass. I also followed Saul to High Halls and he was gone by the time I got there.
Wasn't there a reward when you release Saul? I tried killing and releasing him, but if there was a better reward killing him (don't recall) it wasn't enough for me to reload after helping him.
I ran around the slayer camp and hoped to get in to talk to the goblin prisoners in order to expose Tilian, but unfortunately there is no way to do so.
Barbatos can make weak stat bonus potions without the need for any ingredients, but more importantly with him you can use the Potion of Wisdom yourself (+5 Intelligence), which Allan wants for one of his quests.
Sentinel Island Servant picks....Apparently some people from Broken Valley make it to Aleroth in the add-on (FoV / end section of DKS), or at least you find out what happened to some of them.
The raft was not ready before you got the battle tower, but you could talk to the guy making the raft in the camp (towards the beach, behind where the married cooks were arguing, IIRC) . Apparently he didn't get out soon enough, though (you can find his diary on the raft).