THE DEVIL AND HIS ANGELS WILL NEVER BE RESTORED

Joseph Smith was so emphatic on this - that he would have barred someone from taking the Sacrament for having taught the hellish "doctrine".  The only time I have ever heard someone give voice to the thought, is when they likely were being influenced by the one of the minions of hell, themselves in a weakened, or degraded state:

One of the warnings contained in my book Healing Arts is a quote from Spencer W. Kimball who taught:

"In the days of the restoration there apparently were those who taught that the devil and his angels and the sons of perdition should sometime be restored.  The prophet Joseph Smith would not countenance the teaching of this doctrine, and sanctioned the decision of the bishop that any who taught it should be barred from communion." (Spencer W. Kimball, The Miracle of Forgiveness, 125)  

 Joseph Smith, Sidney Rigdon and F.G. Williams together stated the same:

 "Say to the brothers Hulet and to all others, that the Lord never authorized them to say that the devil, his angels, or the sons of perdition, should ever be restored; for their state of destiny was not revealed to man, is not revealed, nor ever shall be revealed, save to those who are made partakers thereof: consequently those who teach this doctrine have not received it of the Spirit of the Lord. Truly Brother Oliver declared it to be the doctrine of devils.  We, therefore, command that this doctrine be taught no more in Zion.  We sanction the decision of the Bishop and his council, in relation to this doctrine being a bar to communion." (Teachings of the Prophet Joseph Smith, 24)