I think Satan left the building because of Enlightenment, modernist rational thinking patterns and that evil is a manifestation of social problems or mental/emotional dissociative disorders. Basically when science began to rule the roost, Satan no longer had a nest to hatch in.
I'm not one to lay too much power or authority into Satan's account. Satan is not equal to God (or Jesus for that matter). According to tradition, Satan is an angel cast out of heaven. Scripture calls Satan by different names. But they all come down to this basic idea: Satan uses deception, lies, and manipulation to destroy lives. Satan does not make people do things. Satan presents options that are appealing to a person. The individual then chooses to pursue that option toward destruction.
Two cases in scripture illustrate:
Garden - Eve is manipulated to justify her choice to disobey God and eat the fruit. Satan did not make her eat the fruit. She chose to eat it after hearing Satan's reasoning.
Wilderness - Jesus is "tempted" by Satan in three areas. Satan presents a scenario to which Jesus must choose how to respond. Satan did not make the stone into bread and try to feed Jesus. Satan did not push Jesus off the peak. Satan only showed Jesus what was possible and left it to Jesus to choose.
So Satan's modus operandi is to deceive people into the place where they self-destruct. But scripture also lays the blame for the results of that destruction at Satan's feet by calling him the destroyer.
But have we moved to a place where we can prove that the existence of evil is a manifestation of human social problems? No, I don't think we have. Science cannot prove anything that lies in the spiritual realm. God, miracles, angels, heaven, Satan, demons, hell cannot in anyway be proven or disproven through scientific methods.
And to say that Satan is only a metaphor for the corporate manifestation of human evil is to get very close to the argument (which some of the same people would make) that Jesus was just a human and that his divine nature is the metaphor of the corporate experience of his goodness. Or, Jesus wasn't really God. He just made a really great impression on people and still does.
I believe in the person and divinity of Jesus Christ. That allows me a lot of room to accept that there could be a spiritual being who is at odds with God's purposes in the world. I believe that human beings are given free will to choose to obey and follow God's purposes or reject those purposes to pursue other agendas. And I believe that humans are agents to accomplish the greatest good in the world or agent to bring about despicable acts of evil. And if God can ask us to choose to do good, then it is completely realistic that another being who opposes God's will can ask us to choose to do evil.