people disappearing?

You don't moriarty if you have a high science skill you can hack his computer in his office...as for lucas simms and sentinal lyons I don't know...Elder lyonns and paladin gunny you will meet them later on as part of the main quest...hope this helps.

My moriarty left Megaton as well and I don't know where he went along with stockholm and deputy weld left.

Well for me only Jerico left but for lucas simms he is either dead or in the plane above his house (there is a hatch in his house upstaris in one of the corners that take you there) or in his armory and for sentinal lyons she will be at the citadel same as paladin gunny and Elder lyons.

Moriarty was either killed by Lucas Simms in the waste or Lucas was killed by Moriarty so Moriarty runaway but just hack hes .com. (i saw them shooting each other by the minefield I killed Moriarty and Lucas gave me a .44,mag so you mite find moriary or lucas dead ther idont knowbut I think lucas died cause you're game told you to go to moriartys elderlyons comes a lot after this misson

I have the answer for this question. There is a way to find these people and yes even bring them back home. I saw on some websites that some people in Megaton don't exactly disappear but instead are found dead on the ground due to falling off rails and other high places in town. This may or may not be the case in some games. As for people vanishing the reason your quest indicator pointed north into the wastes for moriarty was because thats actually where he was along with everybody else who is missing if anybody. First go inside to sim's house there is a hatch which goes to his roof and then hop onto the railing then hop from there using the pipes onto the higher part of his roof. And from there you have to hop over the walls in megaton into the wastes. There is going to be some visible and invisible ground with plants here don't worry about falling go north where the indicator is pointing and there you would see everybody who went missing so far. To bring them back home get in front of someone and push them back to megaton when at the city entrance door they should walk in by themself if you walk away from them. I tried this myself when I had 11 people missing from town including 3 unnamed citizens and it worked. There is also a video I found to watch on the web on how to get over the walls by doing a search. Its hard actually getting over the megaton walls and might take some patience. I suggest sleeping in your megaton bed before starting this as going over the walls and falling to the other side is going to take some health off.