‘And her lord rose up in the morning, and opened the doors of the house, and went out to go his way.'
Once he was satisfied that the crowd had gone, and unaware of what had happened to his wife, but realising that her non-return probably meant that he would never see her again, the Levite decided to make his escape as quickly as he could. He had presumably been up all night wondering what was happening and hoping to hear his wife's knock on the door. He may well have thought that, in view of her past behaviour, she had chosen to go off with the men.
The affair does not reflect well on him but he was at least glad to be alive and knew that he had to make his escape before the men came back. The reference to him as ‘her lord' may reflect the writer's disapproval of his behaviour. As her lord he should have watched over her interests. Alternately it may mean that the writer agreed with the behaviour that had made ‘her lord', the important one, escape maltreatment.
‘And behold, the woman his concubine was fallen down at the door of the house, with her hands on the threshold.'
Her posture suggests that she had almost made it. Her hands were on the very threshhold. When he found her there he clearly thought she was asleep, and his heart was probably lightened. He was a good enough man not to believe that men could be so evil as these men had been.
“With her hands on the threshold” may indicate that she had almost made it, or that as she collapsed she had vainly reached out for help. She had almost reached shelter, but had not had the strength for the final attempt. It had been too late.