Soy
The dead standing elm is definitely a no go. That being said, the BW heartwood takes a long time to rot. Since you have already cut it, split it down into staves and remove all bark, sapwood and chase down a couple rings in the heartwood. If there is any sign of mildew spots or gray patches, its firewood. If it looks and smells like good old walnut, you should be good. remember Bw likes a wide flat back and you will remove at least 2 inches of material from the back, so allow for that when you split you're staves. Split the staves too narrow, and all you will have is kid bows and arrow materials. If it isn't salvageable let me know, eventually I will get through your area, and I have some primo BW staves. Some are super clean and straight and some are loaded with character. I'll bring you some.
Josh