If we will not be able to escape the evils of war even in heaven, then what kind of heaven is heaven? It is no better than earth. I think this question can be clearly answered if we build on the foundation of the word of God.
First of all, it is important to understand that there are three heavens in scripture (not seven as is traditionally taught by some). When Paul went into the presence of God, he was "caught up to the third heaven" (2 Corinthians 12:2). So where are the other two heavens? I have dealt with this in more detail in other places, so I will be brief here. The first heaven is the atmospheric heaven where the birds fly. It is called the "open firmament of heaven" (Genesis 1:20). The second heaven is the starry heaven; what we think of as outer space. It is scripturally called the "firmament of the heaven" (Genesis 1:14-18) and it is where God placed the sun, moon, and stars. The third heaven then is the abode of God. When God creates "new heavens and a new earth, wherein dwelleth righteousness" (2 Peter 3:13), He is referring to the first two heavens. Righteousness already dwells in the third heaven and it will not need to be recreated. When heaven and earth flee away in Revelation 20:11, God's great white throne (a part of the third heaven) continues to stand.
So now that we have established the existence of three heavens, we need to establish the abode of Satan and his angels. In Ephesians 2:2, Satan is called "the prince of the power of the air." If we think of air as oxygen and other gases, this would limit him to the atmospheric heaven. However, if the word air here refers to open space (as I think it does), it would put him in the first and the second heaven. Ephesians 6:12 warns us, "For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places." The high places are certainly those places of Satan's abode above the earth. Isaiah 14:12-14 describes Lucifer as attempting to ascend above the heights of the clouds into heaven. Evidently, he wants his abode to be as high as possible in order to imitate God. Though there is no definitive verse that I know of, the devil may very well have his abode as high in the second heaven as possible at the door of God's third heaven.
Now, we need to look at the context of Revelation 12:7 to see if we can define the heaven in which this battle is fought. If the battle were to be fought in God's presence--the third heaven; where would Satan be when he was cast out? He would be in the lower heavens. But what does the passage say? Let me piece together some phrases from Revelation 12:7-9: "And there was war in heaven... neither was their place found any more in heaven... he was cast out into the earth, and his angels were cast out with him." We can see from this that the devil and his angels were cast out of heaven into the earth. This would indicate that the battle took place somewhere in the first two heavens and not in the third heaven where the presence of God dwells.
In conclusion, I believe that the war in heaven between the devil and his angels and Michael and the Lord's angels is not in the highest heaven but in a lower one. The third heaven where the presence of God dwells is secure and will endure forever as His holy habitation.