Olaus Jakobsson Stal

I am trying to help a friend find an answer to a question about people from Skaraborg County. Her great grandmother was Lotta Johansdotter and was born June 27,1842, in Edasa, Skaraborg. Lotta married Olaus Jakobsson Stal - born April 1, 1835 in Borgunda. According to former research, they were married April 25 1869 in Borgunda and then left immediately to America April 27 1869. They came to Illinois and settled in Cherry Valley, Winnebago County. We can’t find them in the 1870 census. However, Lotta plus some children are in the 1880 census. She goes by the last name Stahl. It says she is a widow. Some family members think that Olaus returned to Sweden and died there. Others think he left the family and changed his name. Would anyone be able to find out if he died back in Sweden? We can find no proof of death here in the U.S. Thank you!