Hi Evelyn, I'm not related so I don't have any family stories about Simon Hadley Vestal, but I do have a great-grandfather Birdsell who walked away from his family and then had new families with 2 other women in another state using the name Smith.
I've seen your memorial for Simon on Findagrave. He seemed to share with his family the information that he was born in NC and moved to Indiana in 1831, so he must have spoken a little about his past.
The 1850 census, when Simon and Alley and their children were living in Parke Co., IN, has some interesting leads. There is a Thomas Vestal, born about 1814 in NC living in Parke County, IN with his wife and children. Perhaps Simon's brother or cousin? There is also a Ruth "Newlin", age 69, born NC, living with Jacob Newlin age 72 born NC and Zilla Newlin, age 25 born NC. I put Newlin in quotes for Ruth, because an Ancestry member has added the information that her maiden name is Vestal. It's also possible that this is Ruth Newlin Vestal, living with her Newlin relatives. There is a findagrave memorial in Henricks Co., IN for Ruth Newlin Vestal, born 1780 NC died 1858 IN, widow of Benjamin Vestal, whose findagrave memorial states he was born 1776 NC and died 1828 Chatham C0. NC.
The Parke County, IN histories include biographies for several Newlin descendants, including some who descend from Vestal-Newlin families, and Hadley-Newlin families. They all seem to be from NC and all move to IN within that 1825-1835 timeframe.
I don't know if you have previously investigated and discarded these people as not related to your Simon, but I thought I would throw them out there for your consideration.