It is not unusual for a married couple to purchase a tombstone before their death and have all but their date of death inscribed on the stone. It is also not unusual to visit a cemetery and see such a stone with the death date of one individual blank.
If they were born in 1870 they are probably dead.
The question is are the buried in the cemetery or not? It is possible that they were buried there and no one bothered having the death date inscribed on the stone. It is also possible that the person was buried in another location–perhaps with another spouse.
Death certificates, cemetery records, obituaries, or funeral home records may help to answer the question.