Many have long argued that Nightwing, as Batman’s first partner and the original Robin, is the rightful heir to the cowl when the Dark Knight steps down or meets his end. Even DC has backed this notion, showcasing Dick Grayson donning the cowl during moments when Bruce Wayne was believed dead or out of commission. But with one comic, it’s become undeniable: Batgirl Cassandra Cain is the true successor to the Dark Knight.

https://screenrant.com/batman-which-gotham-hero-replace-nightwing-batgirl-op-ed/