The plot is didn't let the spare two who are party of Norman group to go climb the wall instead of Norman, Emma on that day then. the result would be super freaking different. Author want us to know other pieces of info or show another plot or just to increase chapter/episode, purposely dragged more.
if he didn't come back the mother would have known he was somewhere within the walls and that they were still planning an escape, so she would've easily shut that down too so he had to came back to figure out a new plan
Norman isn't lying last episode where krone and grandma we're at the gate we saw flashbacks where (supposedly) krone was on top of the wall and grandma was on the ground basically if there was no cliff krone would have escaped!!!