We will never get that the cranial volume is not the same as inteligence/brain function, or whatever you might call it. Reminder that Einstein brain was smaller than average, and female brain are smaller than male. Phrenology will haunt us forever, in one form or another.

Most likely, some Neanderthals were asimilated into modern humans, most were exterminated in tribal clashes. Reminder also that our almighty specie was almost wiped out from history around 800,000 years ago (https://www.science.org/doi/10.1126/science.abq7487), being the most intelligent organism ever existed.