http://rhesusnegative.net/themission/bloodtypefrequencies/
So if you view the world as one population, then that would mean rh negative blood would go extinct at one point (according to the C-S hypothesis).
If you allow certain groups to control their borders and keep their societies as is more or less, then we continue having isolated populations. If Basque country was to allow Millions of refugees to come in and integrate, then the rh negative blood factor would also become extinct among them.
What we forget in these types of scenarios, people have choices. Who we are attracted to and choose to have children with. It has been often stated, that couples tend to have a high frequency of similarities genetically, so maybe there is something to being drawn to something that feels familiar in others (despite the "opposites attract" theory).
I see the majority of the world population become more and more similar. But I also believe that certain groups like the Basques will likely continue exercising an isolation mindset, at least to some extent. Even smaller groups like the Walsers in Switzerland also continue to sport high rh negative frequencies due to a similar way of life. As do the Bedouins in Sinai.
On a global scale, rh negative frequencies are bound to go way down with an overall decrease in numbers in many high-rh-negative populations and most of the populations bound to explode having low frequencies.
Several studies have indicated higher sex drive in rh negative women (as in women with red hair), so these types of tendencies could also be significant in terms of gene preservation. So overall, I do not see the entire world becoming one population. Possibly for the most part number wise with the exception of regional isolations of certain populations.
Cavalli-Sforza's theory has holes in it. Aside from the Udmurts (where data doesn't appear to be consistent), Scotland seems to have the highest red hair gene frequency with around 0.4 which would make it bound for extinction. It would be interesting to know what the frequencies had been around 1,000 years ago and if this has changed. The Mathieson studies may indicate a drop in rh negative frequencies, but that data is also quite questionable.