PHB ch. 8 states that a creature in a heavily obscured area (e.g. a completely dark area, if the creature does not have darkvision) effectively suffers from the blinded condition. The definition of blinded is "A blinded creature can't see and automatically fails any ability check that requires sight" and "Attack rolls against the creature have advantage, and the creature's attack rolls have disadvantage."
I am a first-time DM running Lost Mine of Phandelver. The party is exploring the Cragmaw Hideout, which is completely dark in most places. Two PCs have darkvision and three do not. In a combat with a group of goblins, the last surviving goblin fled and the party gave chase. I struggled with how to handle the characters without darkvision chasing the goblin through the darkness. None were carrying a torch. Dancing Lights was cast, but they could only be moved by the caster on her turn (I kept things in initiative order throughout the chase).
Per the rules I quoted above, the only hindrance that the darkness gives the PCs without darkvision is that they have disadvantage when attacking, enemies have advantage when attacking them, and they automatically fail ability checks related to sight. The Cragmaw Hideout contains such things as stairs, narrow passages and a rickety bridge, but I couldn't find any rules reason why the characters without darkvision couldn't traverse those just as easily as the characters with darkvision. The rules don't even say that heavily obscured areas are difficult terrain. I suppose I could have come up with some ability checks, which per the rules would have automatically failed, but that didn't feel right either.
Am I missing something that would have made this a straightforward thing to handle?