Ebola thrives in African animal populations, so it has basically forever to do whatever you think it might do - though I'd add that in basically all scenarios viruses become more mild over time. It's not just good luck but because it maximizes transmissibility - killing your host usually means you die too. And that may well be why ebola remains so nasty to humans - we're not its primary reservoir, it's fruit bats which maintain persistent asymptomatic ebola infections, and are often the source of the first human infection in outbreaks.