When working on your "brick wall" ancestor, have you given serious thought to what stage of life they were in when they become your "brick wall?" Were they young and striking out on their own with no responsibilities? Had all their children grown up and left home moving several states away? Or did all their adult children live nearby? Were they a newlywed? Were they the only child living near aging parents?
Your relative did not live in a vacuum and, while people do occasionally "run off and never come back," most people behave relatively reasonably. Your disappearing ancestor may simply have left no records behind of certain periods in his life.