Have you considered tracing the individuals named as heirs to the extent that you are able to do so in the federal census records and then checking to see the last census in which they appear on the assumption that they died between that census and the next census in which they don't appear?
Then try to obtain their death records which are hopefuly available for that timeframe, depending on the state where they lived, using that period as a timeframe.The method is not foolproof as not everybody was necessarily recorded in the census records, but it's an avenue that I've had some success with as long as the parents' names are listed on the death certificate. ( Some states, like PA for example , didn't require parents' names on a death certificate prior to sometime in the early 1900's unless the deceased was a child.)
Problems like these sometimes require a variety of approaches to get an answer.
Other suggestions: (1) Check out cemetery transcriptions in the area if you know where the heir died in the hope that they have a headstone that records their dates to determine a timeframe for a death certificate.
(2) Post the specific names involved on either Genforum or Ancestry.com boards. I was recently contacted nearly three years after a posting on an Ancestry Board and have received and shared information that was mutually helpful to me and the person who resonded to my posting.