I am not sure what you are asking. However, I will throw some answers out and hope one of them addresses your question.
In infectious disease, the paradigm is that the more deadly an infection is, the less likely it is to spread. That's because the infected person dies quickly without having a chance to infect others. I think that there have probably been sporadic Ebola (and Marburg) outbreaks for millenia, but it was never identified because until recently, Africans never traveled outside of their villages much. Thus, the whole village would die and the infection would stop there. Ebola is a problem now because it reached populated, highly mobile areas.
The health care systems in the affected countries are horrible. Without care, the death rate is very high. With care, the death rate is somewhat lower (it is less than 60%, which makes it more mild than past outbreaks). With top-of-the-line care, the death rate would probably be far lower. This is strictly supportive care--electrolytes and treatment of complications.
The short question is what happens when all you medical resources become overwhelm by the sick and dying?
Say it spreads to the US and it only affects .5% thats 1.5 million between that the everyday strain that many health systems are already under you add in the toll the disease itself will take on health workers and what then?