Will some watchers in the book of Enoch be forgiven?
No, Angels have free will like man, but they have no forgiveness as they have no faith. They were created in the presence of God and suffer no memory problems, they know the will of God intimately and have seen His face. For this reason they have no excuses before God.
“And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day”. Jude 6
The Bible does not specifically address the issue of fallen angels having an opportunity to repent, but we can gain some insight from what the Bible does say. First, Satan (Lucifer) was one of the highest angels, perhaps the highest (Ezekiel 28:14). Lucifer—and all the angels—were continually in God’s presence and had knowledge of the glory of God. Therefore, they had no excuse for rebelling against God and turning away from Him. They were not tempted. Lucifer and the other angels rebelling against God despite what they knew was the utmost evil.
Second, God did not provide a plan of redemption for the angels as He did for mankind. The fall of the human race necessitated an atoning sacrifice for sin, and God provided that sacrifice in Jesus the Christ.
No such sacrifice was planned for the angels. In addition, God referred to those angels who remain faithful to Him as His “elect angels” (1 Timothy 5:21). We know from the biblical doctrine of election that those whom God elects to salvation will be saved, and nothing can separate them from God’s love (Romans 8:38-39).
Finally, the Bible gives us no reason to believe that angels/demons would repent even if God gave them the chance (1 Peter 5:8). The fallen angels were completely devoted to opposing God and attacking God's people. The severity of God’s judgment varies according to how much knowledge a person possesses.
“But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more” Luke 12:48.
The fallen angels, then, with the great knowledge they possess, are greatly deserving of God’s wrath. (Jude 6)