I don't really do much in Megaton these days except go to my house, but one day while walking to my house in Megaton I noticed that Lucas Simms wasn't where he normally is, so I go look around the entire town (and sneak into his house) but hes not there, then I talked to Hardin and he doesn't have the unique dialogue that happens when Lucas dies and how he is going to be the Sheriff now. I have no clue where he could be, I heard that there are like glitches that like make certain NPC's fall through the map. Im not sure if that happened but are there any ways to get him back?
Not through the map.... they fall to their deaths from the walkways above. They all have lame armor, and a fall like that will kill them. Stand near the front gate and wait in two-hour increments, or check under all the walkways. I've never had Lucas die on me, but others certainly have.