Fingers crossed the second cousin will test. There’s a line in my family that daughtered-out unhelpfully too.
I tested my MDNA in the hope of (eventually) uncovering about that line. It ends for me with a Mary Mahony who died in 1908. I have not been able to find her marriage, but I have it pinned to a 2 year time frame, as she was the second wife of her husbands, and I know when the last child was born to the first wife. She came from Co. Clare but I don’t know where.