I haven't found any reference to his death in Johnson County either.I have several different transcripts of the three Adams Cemeteries and he's not in any of them unless his stone is no longer readable. Neither is Susan Walser to my knowledge. The only other son of Jacob Adams that was known to move to Johnson County that isn't listed in any of the three cemeteries is Jacob Adams Jr.Which is interesting because one of those cemeteries was known as "Jacob Adams Cemetery" at one time as it was located on property he owned.
You can see the land patent for an Isaac Adams in Pettis County at www.glorecords.blm.gov. It's the Southwest quarter of the Northeast quarter of section 20, township 48N, range 23W.It's in the Western part of Pettis County so not too far from the farms of the other sons of Jacob Adams in the East of Johnson County.Unfortunately, there were also some Adamses that moved into Pettis County from Cooper County along with some Ellis families they intermarried with.I have not found any indication these two Adams lines are related.
My sources for anything I have on Isaac and Susan are iffy.Mostly gleaned from the LDS Familysearch website.From what I've found on the other children of Jacob Adams I figure the LDS info is about 80% accurate.I do know from a transcript of Wilkes County marriage bonds that Isaac Adams married Susanna Walser on 30 July 1813, Eli Pettey Bondsman, J. W. Pettey Witness.There was also a marriage bond between an Isaac Adams and a Sintha Roberds on 18 Oct 1817, John Roberds Bondsman, W. W. Martin Witness.The way these Adamses used the same names there is no way to determine from this if these two Isaac's were the same, related, or total strangers.
If you have the names of any of John Walser Adams' siblings and their offspring that you could share with me I can check the cemetery transcripts that I have and see if any are there.Also, if any of your ancestors moved to Washington Territory around 1889 I'd like to hear it too.