Paabo recently told a conference at the Cold Spring Harbor Laboratory near New York that he was now sure the two species had had sex — but a question remained about how “productive” it had been.
“What I’m really interested in is, did we have children back then and did those children contribute to our variation today?” he said. “I’m sure that they had sex, but did it give offspring that contributed to us? We will be able to answer quite rigorously with the new [Neanderthal genome] sequence.”
That's pretty much a non-answer answer. Maybe it depends on what the meaning of "is" is?
We'll see soon enough, I reckon.