Darrel Nichols, 20, Park City, 1 April 1973
Thought I’d answer your question.
Two obituary links on Newspapers.com for Joseph L. Nichols (father of Darrel B. Nichols)
*** The obituary says he died of natural causes in a nursing home.
The Daily Herald (Provo, Utah) 06 Apr 1973, Fri Page 4
6 Apr 1973, 4 - The Daily Herald at Newspapers.com
Deseret News (Salt Lake City, Utah) 06 Apr 1973, Fri Page 63
6 Apr 1973, 63 - Deseret News at Newspapers.com
Two obituary links on Newspapers.com for Willard T. Nichols (uncle of Darrel B. Nichols)
*** The obituary says he died at home of a heart ailment.
The Daily Herald (Provo, Utah) 18 Jul 1973, Wed Page 4
18 Jul 1973, 4 - The Daily Herald at Newspapers.com
Deseret News (Salt Lake City, Utah) 18 Jul 1973, Wed Page 55
18 Jul 1973, 55 - Deseret News at Newspapers.com
NOTE: It seems the family many have had a predisposition to heart problems.
Possibly the reason for Joseph’s death.