In "Bounty Land Warrants Go to Heirs Not Debtors in 1859," I mentioned a newspaper article from 1859 that discussed briefly that bounty land warrants were to be treated as personal property in estate settlements and what the process was for obtaining a patent to federal property if the warrantee had died before the warrant could be surrendered and a patent issued.
This image comes from a few years before that (1853), but the process was similar. The heirs of James Kile had to submit proof from the court that James had died and how his estate was being administered.
This petition from August of 1853 is one of the statements from the court that is contained in the surrendered bounty land warrant file for War of 1812 veteran James Kile.
Fortunately, Mercer County, Illinois, is not a burned record county, but if it had been this file would have been an excellent location to get some of the material regarding the settlement of his estate--particularly the names of his heirs.
If any of your elusive ancestors died while they were "in process" of a federal land claim, there could be local court documents in their file. Another relative was paying for federal land in Ohio on credit in the early 1820s when he died and there is mention of his estate settlement in his cash purchase file-unfortunately it's not as detailed as the documentation in the file of James Kile from 1853.
Did any of your ancestors die while completing a federal land claim?