Reason Randall Was Spared
We know Randall could easily have been devoured by the monsters after they taunted Boyd into having to decide whether to save the people in the ambulance or help Randall.
Apart from the fact that the monsters were taunting Boyd at every turn at that time, it always seemed there was a bigger reason that Randall was spared, that he had some important part to play in the story cycle that lay ahead.
Now Randall is helping Julie storywalk, and really is the only person other than Ethan who seems to know that Julie can and is doing that. He's definitely the only person actively helping her do it.
MiY could easily have killed Julie if he wanted to when he killed Jim. Or he could just hang out near the old fortifications where Julie storywalks and kill her there, or just about anywhere he feels like. MiY seems pretty unconcerned about Julie traveling in time ("we have to stop meeting like this") and that's not only because he's confident she cannot change the story, but her actions might be essential to the outcome MiY wants.
Julie might have an important role to play to close out this cycle from MiY's POV. And because Randall is helping her, he was spared. Maybe Julie wouldn't be storywalking like this without Randall's help.
However, maybe MiY's arrogance will catch up with him this time. Maybe Julie will do something different and unexpected and Randall will have been one of the major reasons she was able to do it.