Dolly , Are we to assume you have written to New York state vital statistics, and they have not found the marriage and birth. and that you are positive they took place in New York. ? Have you considered the above could have happened in states around New York and anywhere on the way to Iowa. I wouldn't be concerned at this point trying to find him in Westphalia until I pinned him down in the US. Often when a person more or less disappears it is possible they came over to work/checked things out and returned back to their home land for a time. He could have returned, married there and had the child there. You have only a small obit, there may be a larger one written up in any of the German newspapers published in the area at that time, or even a larger one in a different edition of the newspaper the small obit came from. The death record may be of more value. As often there is a question, if the person was not born in the the US, how many years in country?(at least in Wisconsin). Probate ,tax records and voter registration should be an assist.
Jane