No, fallen angels cannot repent. They have been given over to their sinful rebellion. Repentance is something granted by
God to people (
2 Timothy 2:25) and is part of the work of
salvation that is the work of God. Angels have no way of being redeemed, that we know of biblically, because the pattern of redemption involves the
incarnation of God where he became one of us and died for us. This means we are able to be redeemed by the sacrifice of Christ, God in flesh (
John 1:1,
14;
Colossians 2:9). But there is no such redemptive work supplied to the angelic realm. Therefore, there is no regeneration and no change, which means no repentance.
The Bible speaks of elect angels or chosen angels. "I solemnly charge you in the presence of God and of Christ Jesus and of His chosen angels, to maintain these principles without bias, doing nothing in a spirit of partiality." (1 Timothy 5:21). So we can see there were chosen angels. This probably means that God was electing angels not to fall in the great spiritual rebellion before the creation of the world. If they were chosen to not fall, it was probably for a reason to serve God. We as humans were not chosen by God not to fall, but we were chosen to be redeemed (
2 Thessalonians 2:13;
Ephesians 1:4-5).
So, fallen angels cannot repent, be saved, and spend eternity with God. They knew God in the spiritual realm, rejected him, and will face their just punishment.
http://carm.org/can-fallen-angels-repent-and-be-forgiven