Angels Receiving Punishment
Moshe Ben-Chaim
Reader: I just read your essay on Angels, but I still don't understand. Do angels have free will ? (Non-Jews say yes). What are archangels?
Mesora: I will explain angel's will below, but Archangels are not a true phenomenon.
Reader: Once Hashem creates an angel for a specific purpose, is it destroyed when its mission is completed?
Mesora: You could say so, when referring to "angel" as a natural force. One could term the cessation of such a force ( a completed mission ) as a "destroyed" angel. A better description is, that it was created for a specific time frame, not to exceed that time. So its "life" was destined from the outset. G-d did not discover something new, realized it is no longer needed, and then destroyed it.
Reader: If your answer to the question of angels having free will is negative, how about the "fallen angels" of Genesis 6:2. What are they?
Mesora: I am not certain about free will. The Torah does seem to depict angels as having will, as the Torah discusses Lot and Abraham talking with them, and they respond. One is even punished as he ascribed the miraculous phenomena of overturning the city to himself, and not to G-d. The Rabbis wrote that statement to teach a problem with ascribing miracles to anything but G-d. I would explain the two Rashis (Gen. 19:22) as teaching us exactly that.:
(Gen. 19:22) "(The angel said to Lot) Hurry, escape there, for cannot do anything (destroy Sodom) until you come there..."
Rashi 1: "This is the punishment of the angels, on account that they said "for we are destroying (Sodom)', and they ascribed the matter (destroying Sodom) to themselves. Therefore, they did not move from there until they righted, and they said the matter was not under their control."
Rashi 2: "...for two angles are not sent for one mission".
What does Rashi 1 teach? The angels didn't truly talk, ascribing phenomena to themselves. However, the Rabbis have license to write these medrashim - stories - teaching us fundamentals. Perhaps here, the Rabbis desired to teach a new lesson; that G-d alone caused the destruction of Sodom.
Somehow, there was room for misunderstanding the cause of Sodom's destruction. An angel - a "force of nature", like fire - will sometimes appear as a purely natural event. But as Rashi said, the punishment of that angel was that "it didn't move from that place until it admitted that it had no ability of its own to perform the destruction". The angel - the destructive force that overturned Sodom - didn't necessarily talk. When the angels said, "we are destroying Sodom", this means that the force of nature causing the destruction, seemed natural. It appeared to "claim sole responsibility" for Sodom's destruction, with no will of G-d. Therefore, its appearance required correction, in some manner. There was something about what took place in Sodom, that onlookers might ascribe a natural disaster to Sodom, thereby forfeiting the lesson that it was in reality, a divine punishment. Hence, no deterrent for future generations would exist. Angels, or natural forces, can only function by the will of G-d, and not independently. The destructive appearance somehow had to be altered so a warning to others would have the desired effect. The fact that the angels "remained until they corrected themselves", means that within this disaster ordained by G-d, there was some element which clearly indicated that it was of divine origin. What that was, I do not know, but it was part of the disastrous process, as it was the angels - these forces - which also corrected the previous error.
The next Rashi says "two angles are not sent for one mission". This means that angels are forces of nature, as such, have specific properties. Therefore, water cannot burn, and fire cannot moisten. Each having its own properties, each has a "singular mission".
We see from these medrashim that the Rabbis desired to teach us insight into the truth of things, but did so in a manner that only those intellectually prepared will understand them. Someone of infantile thinking will at the least, remember these amazing stories due to their startling, manifest content for a future time when ready to interpret them.
Regarding your last question, Rashi says "bnay elohim" are not 'fallen angels', but a term denoting sons of officers, people in high position. Perhaps this verse attests to the seeds of error of the generation of the flood which ensued. Those seeds of error were egoistic drives, stemming from their high positions in government.

See the article on Angels for more on this topic.