How did the man on the roof escape the roof after removing his hand? The only access door was locked to keep the zombies away from him and it was still locked and the chain had to be cut so the hunans could get up there.
I recall that Rick and Glenn jumped between roofs early on or went over some gangplank or something. They also climbed up a ladder on one (hard to climb down with one hand and a bloody stump....)
Maybe that helicopter Rick saw picked Merle up....
Merle will probably reappear at some point - too good a bad guy with too justified a grudge to just have him disappear forever.
Am looking forward to this Sunday's episode. It gets curiouser and curiouser....