I don't think that scenario produces the picture we have. Neither apparently do most scientists. Most people still don't have the virus, but if its ancestor had been in Europeans long ago, all people of European descent would have some form of it.
... Or they'd have the immunity, I should have said. Introduced in humans in pre-tech times, the virus would have created a huge death rate until either 1) a milder form of the virus evolved or, 2) humans with the immunity mutation were the most common kind of people around.
We don't all have the mutation (most of us have neither the mutation nor the virus), the virus has a high virulence, and genetic analysis points to a recent introduction in humans.
Like we all have some form of smallpox?
That means that protection is passed on to only 3/4 of descendants. 1/4 are left unprotected. As long as no epidemics come around eventually a large percentage of your population does not have the protective gene ~ and so they die.
In a number of cases it is disadvantageous to inherit the autosomal recessive protective gene from both parents. They die shortly after birth (under paleolithic conditions) ~ or in modern times they don't die right away but suffer as with cystic fibrosis, or sickle cell disease. With CF the current belief is that this is the gene that saves some humans from the ravages of the black plague. With sickle cell, that protects against malaria.
Like a time machine eh!