I am so glad that your neighbor was looking out for your family that day! Accidents happen quickly, AND please stopped blaming yourself! This had a happy ending, thankfully. Baby gates are one of the best ways to ensure your yorkies will be safe.
I have not had this happen, because I am on the second floor. Id Suzi ever tried to run out, she could go up and over the Balcony.
BUT, When my son was a toddler, he got out in only a diaper , running down the sidewalk. YEp, my human baby did that. I never forgot the terror I felt. A neighbor found him, and luckily he was fine . I never ever got over that.
If suzi were to get out, I would rather die then to have her hurt , or killed.
Same with my son, he is now a teen.