Yes, you need to split the level into at least three parts, where the first and last ones create an unnoticeable joint (or, just always have three instances of one seamless level).
If dynamic objects are in a sublevel that is loaded/unloaded (Level Instance Actor) - then you may encounter a situation where your NPC followed you and then simply disappeared before your eyes because the sublevel to which he belongs was unloaded. This also applies to items that the player can take with him.
Your level is straight, you just constantly load a copy of it in front of the player (and unload the same one behind his back).