I am sure that some of the old gods did survive and even became part of Sigmar’s pantheon, Taal was mentioned being worshipped in Ghur while Myrmidya has her own knightly order.
Gazul and Valaya were very likely alive at the time of myth but some things had happened to them, like, it was mentioned that Gazul was defeated by Nagash but part of him still preserved by his worshippers.
Kurnous seems very likely survived and got name changed for copyright issues, Khaine was half-dead but there is still chance for him to rise again though little. It was also mentioned that Teclis was trying to revive other old elven gods.
Lizardmen’s gods, aka “old ones” seem also still exit in AOS, they, such as Sotek, are now “star gods” who were constellations and still able to bless Space Lizardmen. It is interesting that Sotek even has human worshippers now.