When they left Earth-51, our Jason was all depressed and shocked that Bruce had got killed and that he'd killed Joker, and so he went back to Gaslight!Gotham where he'd felt so at home. I don't know who took his place, but our Jason is getting better in Gaslight!Gotham, with Bruce and Ted and the Birds and the blond-haired, violet-dressed young woman Batman and Jason saved.