I'm sorry. Crows are fascinating and clever souls, each an individual and, in my experience, quite a character. I salute your Onyx. May his memory be a blessing. Wildlife rehab is hard and I salute you for doing it.
My Onyx died suddenly of a heart condition in 2018. He would not have gotten along well with your Onyx, I'm afraid. My Onyx enjoyed performing his imitation of a lamprey, and he had a keen interest in music.